Here's the set-up - you have an undead person - vampire - and the police take DNA to rule this person out as a suspect. *They* don't know the person is undead. Would one look at the DNA make someone scream - this is from a dead person! Or would they only see the markers and say - no, no match - and the whole deak/alive thing not even come into play?
ETA: Daaamn you people are fast! I've got my answers but of course curiosity would welcome any and all info anyone wanted to toss my way.