Well, we have one undead npc, don't remember his name, but you meet him as soon as you cross draw bridge leading out of Fort Joy.
As for undead as playable race, they will probably look like skeletons, and you will be able to pick up from what race your char was when he/she was alive. That is why, i think, undead is absent from the game's art, since you can be undead from one of the 5 races, who they will draw?
From what i understand undead will be able to conceal their condition, kind of like worgen in wow, but when combat starts it will fade. But it is my speculation.
Personally, i am more interested in the undead origin itself, since it was written by Chris Avellone.
