You all seem to forget the fact that DF vampires are DF vampires. DF has quite a unique lore and gameworld. Show me a common fantasy world where elves eat killed men and still pass for animalistic treehuggers? Same for vampires, they may be any...
As for the differences: dwarves almost never see sun (at least in many of my fortresses) so they are naturally pale, also they are covered in dust and mud. In such situation it shouldn't be too hard to hide your "undead" appearance.
And while DF vampires never age, they should still grow the nails and beards (even on corpses those tissues grow, and judging by how vampires probably will have regeneration, all the tissue growth stays).
I am more interested in those facts:
In this case, the plan is to then have a witness to a bloodfeeding be able to report that to a guard/sheriff/etc., and then that'll be available for you when you decide on somebody to accuse/arrest/punish. You'll be able to accuse the wrong dwarf, and we might have the vampire or grudge-holding dwarves level false accusations that'll muddy the witness accounts a bit.
Vampires that are hiding their identity in your fortress will intentionally walk at normal speeds and their historical kill lists will be hidden, although you might spot them running fast if they are in your military and fighting with an opponent.
Holy crap, it's like you're the AI monitoring crew trying to find a changeling, and a random assistant yells "captain is a changeling" and a bunch of guards go down on him with fire extinguishers and batons and space him... Sorry if you didn't get the reference
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