A bigger problem is that ALL gods create vampires, not just gods of Death & its related spheres. Gods should be able to apply a wide range of sphere-appropriate curses.
And even bigger than THAT is the fact that vampirism & lycanthropy are allegedly inflicted as punishments, when in actuality they're major buffs. (Well, the lycanthropy is a punishment when you calm back down & realize that you've killed your family, but physically it's still a buff.)
Until those undergo a major rewrite, nitpicking temple zones seems kinda pointless . . . but watch as I go ahead & do it anyway. One item that NJW2000 overlooked was if there's a priest assigned to said temple. Such a priest could get a divine sensation that an abomination was trespassing on holy ground, and then come out be all "This is MY church!!", which would most likely help identify the vampire. True, this could still be "gamed" (there are almost always useless dwarves around that can be appointed priests), but at least we would HAVE priests. The system could be made more effective in single-god temples, so that too could be a delaying factor--I get the impression that even many mature forts have only one Unitarian church.