Depends on the Orc.
I'd imagine the Orcs to be into ancestor veneration. They may not "worship" any gods but may have rituals to honor Clay and Flow, perhaps reskinned a little depending on the tribe. Animism and witchcraft may be quite common. The Isir have their crazy serpent thing going on, you could play that up into a sort of religion. Maybe there's even a demon-snake monster that they worship!