RTF is a global modification that replaces all towns in the game.

There are a few options here:
1) Atheists (like Orcs, Mages)
2) They worship Shalassa (so what if there are Nagas?!)
3) They worship Shalassa and Sillane (dirt - earth, swamp - water, etc.)

I would make it so they worship spirits like the Orcs, but some kind of evil spirits (which is why they don't get along with the Orcs). Let's say some powerful water spirit from the spirit world.