I went and checked out the stuff on Play Online Viewer, and it said Promathia bound himself in chains to put limitations on his power. There was no mention of him being the creator of the beastmen. He may be a dark god, but his official title is God of the Twilight, which does seem to imply that he's evil, but there's the chance he's not.

I'm more interested in the Emptiness and the Empty monsters. They look freakin' cool, and the screen shots of the Emptiness just look absolutely awesome.