Also, seduction, assassins, usually not worth the time. There are exceptions. But look at this unit:
http://dom3.servegame.com/wiki/Rakshasi
A 350 gold unit who can turn into in a seducer/assassin. Cap only. Not that strong in a assassination. You could use her as an assassin, but the chance of losing her to bodyguards, a well scripted mage, or even patrollers is just to high. It would be hard to get a good return on investment on the 350 gold. By using her in a assassin role you also lose a capital fort turn, a research mage etc.
Better (but not great, it takes blood 7 research to get one) is:
http://dom3.servegame.com/wiki/Samanishada
No seducer, but it is summonable. Reasonably cheap in CBM. ("only" 20 blood slaves). So cheaper, only uses a mage turn* and not a capital fort turn. Already has equipment. (The seduction mage above has no armor). Sure he cannot seduce, nor selfbless. But it is better at killing enemies. Also give him a Spirit helmet and he kills most enemies in one turn. (This tactics is especially great when you use it against enemies siegeing a castle. kill all the commanders and the sieging force autoroutes during a break siege. Also you can sneak the assassins in, so you don't need that many. (As Lanka is a nation with access to air, it can forge air boots).
Yeah, I'm giving away my own tactics here.
But these are the kind of things you can expect. So if you expect assassins bring some cheap indie commanders along.
Edit:
*: note that this isn't totally true. To get the 20 slaves you also need to spend a few mage turns. But even a few mage turns < capital fort turns.
Also note, not everybody has capital only mages. So not all the capital fort turns are that valuable.
Also note 3, I tested some stuff, and I'm not convinced anymore that the site% directly affects the blood hunt chance. At 0% sites it was still easy to find slaves. So there is that.