Well, they're not mortal races of Nirn, so vampirism can't effect them. But, the script only prevents vanilla vampirism(or vampirism mods working off of vanilla), so using a alternate vampirism mod will allow them to become one.
I tried testinghall and my character, a daedra seducer from RBP and he did turn into a vampire..however I'm planning to install a Vampire mod, not sure which, probably will wait for the release of unholy darkness...in the meanwhile I'm having a look at the other mods around...have u got any personal preferences about these?
Cheers