Actually, we learn a lot about Raszagal through Zeratul. Not only does she say she's a kindly soul, but his past of being a wanderer speaks volumes. Raszagal apparently saw little reason to restrain Zeratul or ask him to stay on Shakuras to fill some sort of authoritive position. She thus is showing perception by not putting Zer in a position he can't fill, and also kindness and a relaxed hand by letting him go where he wants. In a clear parallel to the Conclave, she doesn't demand people follow strict guidelines. The Dark Templar in her command more or less do whatever pleases them, as long as peace is maintained.
This makes Raszagal a very peaceful type of leader: the Steward. The Steward's key word is maintenance -- keeping things the same way as the Steward envisions. Unlike the other leadership types, the Steward is primarily past focused. The Steward is not as dynamic as Visionary, and isn't about going toward some golden future, nor is the Steward necessarily ready to step to the plate for emergencies like the Strategist. All the Steward really wants is a peaceful life, for herself and for her people.
This is shown in Raszagal's comments about Aiur. She's glad that the Dark Templar and the Khalai Protoss have the chance to be united again, and she looks back with longing on her memories of Aiur. Yet, at no time in the years prior to Starcraft has she ever advocated either going back to Aiur and taking a part of it by force, or establishing some sort of diplomatic mission to reach out and reunite with the Khalai 'Toss. Granted, neither might have been possible, but Raszagal shows no sign that she wanted to take either path. Her focus was more on caring for her people, rather than taking risky action in an uncertain endeavor. In fact, given that the Dark Templar are living on a planet where a Xel'Naga temple is, they're staying there just to study the past, rather than looking forward.
Stewards are absolutely not endeavoring. This is the primary reason they don't seem like natural leaders. Actually, Stewards seem more like leaders than Operatives do. Stewards work the best when they are trusted by those around them, and preferably loved or respected. More so than other leaders, they are influence based. They respond to others on an emotional level, even if the Steward isn't himself emotional.
Raszagal is very emotional, though her years of existence have tempered her to the point where any extreme emotion is outside of her character. However, her normal level of concern and peaceful ambiance allows the Dark Templar to trust her. She earned Zeratul's trust by keeping a relaxed hand. The Steward might not seem like a leader, but there are certain types of people who need that relaxed hand in order to operate and allow their natural creativity show.
Stewards are excellent peacekeeping leaders, and are great for keeping Visionaries in line by reminding them that the past exists for a reason, and that not everything that is old is obsolete. Computers go obsolete, but history does not. Some traditions are wrong, but others are beneficial and provide for a happy culture -- they give people more to do than just live day by day.
Stewards are best are reminding people of who they really are. The thing about relaxed authority is that it allows others to show their true form. Laid-back leaders let people to find out if they are the sort that takes initiative, or the sort that needs prodding to actually get things done. It can let people find new ways of performing necessary tasks, and let others realize what tasks are more important than others. When you have to step up and choose for yourself, you begin to realize your strengths and failures. Stewards who are more experienced and mature know how to observe those under them and gently guide their followers based on what they see. Raszagal is this sort of leader -- or would be if Kerrigan hadn't taken over her brain.
Because Raszagal is such a small part of Starcraft, I'm forced to use alternate examples of Stewards. Though it is good to see different sides to Stewards. Again, I'm hopping back to Lord of the Rings. One is obviously Steward Denethor, who is past focused in that he wants the city of Gondor to remain glorious as it always was, and for his sons to rule Gondor after him. He was so focused on the past and what he wanted it to be that he didn't even want the true king to come back. Denethor's emotional influence is to do things like wear chainmail under his robes, sending a signal to his men that they need to be strong and always ready for battle. Until he loses his mind, that is.
But you know who is also a Steward type leader? Barliman Butterbur. That's right, the guy who runs around serving beer and forgetting wizard's messages. He's past focused in that he wants his tavern to be, and he influences his workers emotionally by not accepting nonsense, but showing fairness in all his dealings. He's friendly when he needs to be, harsh when times call for it, and humble when he does wrong. He might not be a knight fighting for Gondor, but Barliman is a good guy, and his simple honesty makes him a worthy leader, if only when it comes to pints and stables. Anyone in the inn business would do well to follow his lead, and he likely exudes an influence that he doesn't even know he has.
That's the thing about Stewards. Their example and patience makes them trusted by those who are around them, even when the Steward isn't technically leading them anywhere. When a Steward gets impatient or becomes a bad example, that is when they fail, and others fall away from them. Thus, a Steward must try to be morally upright, at least comparably to his contemporaries, and in the matter of his career.
Raszagal shows her uprightness by her calm and lack of anger towards the Khalai Protoss. She welcomes them to Shakuras without objection, and does not question Zeratul for bringing them to her planet. This serves as an example to the rest of the Dark Templar, who see that their patient leader is being merciful and want to do the same. Her example causes the newcomers to trust her, as she is choosing not to punish them for exiling the Dark Templar so long ago. Even the plenty arrogant Aldaris is calm in her presense, at first, and probably would have remained so if it weren't for Kerrigan.
People tend to underestimate Stewards, or else underestimate how much the world needs Stewards. Because of their static nature, they don't seem as brave as others, and can be seen as stupid or inexperienced. Raszagal is not generally a favorite character, and Barliman is considered thick. However, when both of them were in their heyday, they were good leaders who considered their options. As was Denethor, but he deserves some of the crap people give him. What made all these leaders good in their time was their ability to send other people out on missions and to gather information. This is why Zeratul is so important to Dark Templar society; he acts on Raszagal's behalf, and serves as a source of information and aide.
That is what all Steward leadership hinges on: trust. When a leader is laid back, this reveals not only good followers, but bad ones who will take advantage of a laissez faire situation. When followers don't trust or don't care about the Steward, things can be iffy. Though most Stewards, either through expertise or personality, can draw people to their side, those that don't can be devastating. The Steward won't necessarily know how to handle that. Any time a Steward tries too hard to force someone to listen to them, it comes across as pompous, because that is the opposite of their nature and not really what they should go for. If the Steward by their subtlety cannot convince anyone, then they're better off letting that person remain unconvinced, and then showing by their actions that they were right or at least morally sound all along.
Raszagal does not argue with anyone. Prior to the events of Starcraft, she believed that either the Khalai 'Toss would come around, or else she would go on more or less ignoring them for the forseeable future. Even under Kerrigan's influence, she talked down Aldaris rather than discuss logic with him. Stewards, like Visionaries, are absolutely not detail oriented. They don't like useless pondering or inane puzzles. They prefer to deal in reality. So long as their goals get done without any serious moral failures or tricking the general population (or reluctance to be immoral, in the case of Steward leaders who aren't so ethical), the Steward doesn't really care what the details are.
Stewards want a sort of realistic fantasy, where they are successful and the people around them are happy. Even more so than the Strategist, the Steward's self perception depends a lot on the surrounding people. Obtaining their fantasy means not contradicting wayward or mistaken followers perhaps as much as they should, though Raszagal seems to have obtained a level of trust where most people believe in her wisdom, judging by how Zeratul follows her.
The unique thing about a Steward is that they can exist properly at any level of authority. They can be high, low, and middle, so long as their individual maturity level is developed enough for their position. Any position they can get where they have the ability to keep a loose watch over and trust their followers works well enough for them, at whatever level it is.
At the end of the day, Stewards are very necessary to life, and are generally sources of protection for the creative class. While they can be too open to new ideas or new "morals", they're generally very calm and easy to talk to. At least when they're old enough to be understanding of the world and be mature, like Raszagal.
A relaxed leader who allows his followers free reign in completing tasks.
Key words: Maintenance
Authority level: Any
Operates best: In a state of trust with the followers
Operates worst: When expectations are high and trust is low.
Potential weaknesses: Extreme moral laxity, lack of critical observation
Ultimate vulnerabilities: Subject to the opinions and feelings of the followers.