Bump for new version, here's a quick summary:
"As of 0.9, there are now 3 types of necromancer, listed below (all can animate corpses, due to hardcoded mechanics):
Necromancer (Lern Secret from god, tablet)
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L Dark Sorcerer (Buffed version of vanilla necromancer, can use curses to slow/weaken enemies)
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L Summoner (Can turn corpses into 3 special "demon" types, has the least physical ability)
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L Lich (Turns into an extremely durable and strong form which can fly, zombies are weaker/slower to compensate)
I wanted to do a necrotizing gas blast, but apparently dwarf fortress doesn't want to co-operate with me, so dark sorcerers get curses instead. It's just as potent, trust me, when you have 4 necromancers all cursing you from a tower (because apparently they can see outside it), those zombies will look a lot scarier. Also, if you find an empty tower, it seems to be because a god/demon created a tablet and put it there."
Again, have fun. Liches will probably be really fun in fortress mode, their bones are as hard as steel, and they have no blood.
All the types DO appear, though due to the uncommon occurrence of towers, you will likely only have one tpye per world, and it may take a few worlds to get what type you want.
There have also been a few balance tweaks, such as the 2 lesser vampire types without speed abilities have had passive speed buffs applied to them, and there have been numerous bugfixes and cooldown tweaks. Ancient Vampires also create master vampires when they bite now.