They should be fine, but i've kept guinacara sterigoisi group with my old rays and it did not end well. Keep an eye out and have a net ready if you start to see soars on the rays' discs or if you see the tailes all chewed up, get em out of there. If you feed them black worms, blood worms, or even small earthworms, they might mix one up with a rays tail. A small burried ray with nothing but their tail sticking out looks allot like a worm to a little cichlid.
Also depending on size, they might get eaten. If you're talking about adult motoros, I wouldnt do it.
Good luck!