CptAlfr

According to the vampirism guide, when you have a Hunter Coat equipped vampires should take damage upon biting you.
I have tested this on the server with multiple vampires, and every time it acted the same way as it would with normal armor. I would take a slightly reduced amount of damage (and poison if they had poisoned fangs),but nothing would happen to them. Also vampire NPCS are able to bite you from behind when you have this armor on, so I don't know if anything is intended to happen with them or not. I have not tested this on a single player LAN world though, so it could be a problem with the server and not the mod.