The response depends entirely on the NPC! The gravedigger and the bartender both will attempt to fight off the attacker, and the receptionist and the waiter will try to evade. None of it is terribly effective if you're trying really hard, though.

Successfully drinking their blood does work as real blood, but it's sort of... weird. It has a strange taste, like maybe it's a little old, and it will make the drinker feel sick in a hungover sort of way for a few hours with some bonus nausea thrown in for fun.