That's pretty much a given!
But it is defined to the extent that applying the vampire template makes a character Evil, and presumably being Evil Undead will make Durkon's continued career as a cleric of Thor...difficult. The author is free of course to ignore these rules and restrictions; its his world and his story. But I think the audience could legitimately cry foul in that case, especially given that we've recently(ish) had Redcloak give Tsukiko a lesson on the nature of the undead in OOTS.