Well, first of all, they get powers that turn them invisible. That one's obvious. Then you have a raise dead power, which is good when you get mobbed (since you probably don't have heavy armor). All in all, the vampire has lot's of characteristics that synergizes with assassins. Personally, I don't like to use it since i don't wanna hassle with drinking blood, but it's very viable to an assassin. Hope this helped!
