Okay, let’s look at some of the “gods of the dark folk” as Monster Mythology puts it. Of all of these, only Squerrik, the wererat god, has any sort of clerical class, and those are just shamans. I’ll address him in a separate post about shaman-only gods. I’m a bit iffy on which of these should have priesthoods, but I think it does make sense for some of them.
Cegilune – This is one I’m not sure of. Hags fear her, but some might still want to be priests. However, I’m not sure whether she’d care to grant spells, or if it is even appropriate for hags to become priests. I’ll need to review their entries in the Monstrous Compendium.
Kanchelsis – Vampires can be clerics, so I’d suspect some would worship him. There may be some crazy humans who do so as well, in the hopes of becoming a vampire. Priests who become vampires could also fully embrace their new status and switch from their old god to his worship, so again, seems reasonable he should have priests.
Mellifleur – Wizards who want a boost in their progress towards lichdom might choose to become dual or multiclassed specialty priests of Mellifluer. Priests who wish to become some form of priest-lich could worship him, too, or they could be mortals who wish to help wizards become liches. He could also be seen as a general god of Necromancy or undead. This would fit with Velsharoon in the Forgotten Realms, who is a separate god but holds Mellifleur’s alias there.
Balador – The god of werebears explicitly does not have priests, but he intercedes on the behalf of priests so they can continue to be priests of other gods. It may be reasonable to make werebear followers of Balador into sort of a sub-set of priests of another god, perhaps various good lunar deities, similar to Meilikki’s worshippers in the Forgotten Realms.
Ferrix – Weretigresses don’t seem much like the type to take up an active priesthood. She might have a small group of ranger-worshippers though.
Daragor – Werewolves are brutal, evil creatures, but they’re not tribal. If they have any form of priestly worship of Daragor, they’d be priests and not shamans. I’m not sure if Daragor would care enough to grant spells though.
Eshebala – the goddess of werefoxes might have a priesthood, primarily to serve her vanity. I’d imagine they’d have to frequently praise her beauty, cunning, etc. in order to stay in her good graces. She certainly seems to care about her followers, even if it is primarily to receive complements and flattery.