Actually, it is, considering that Fallout 3 was the only game of the series where they appeared (and even then, they were more cannibals than vampires).
While we don't know for sure I'd say that it's pretty difficult we'll see vampires in the game.
And that's for the best, if you ask me...
Yes, but the only reason they appeared is because Bethesda were making the game. I know that the original developer's(Obsidian) are now making the game, but Bethesda is still they're publisher and Obsidian is using they're tech.
And they are certainly NOT cannibals, don't you remember the Laws.
I also hope that cannibal perk will make a return, that was awesome!!
Anyway, I hope the Dev's answer my question, since we all are just speculating.
But no mater what, can't wait for Vegas!!