I would not keep him with your ray... my rays will eat small fish (my 10" female has eaten 4" goldfish) and I have to say my ARTC ate almost right away... he hangs undernearth a piece of DW or pvs in my community tank and so far has eaten... live blackworms, NLS thera a, omega prime reef flakes... and likely some of my tetras soon if my 56 doesn't cycle in time for him lol...
and with marks like that he is undoubtably stressed.. maybe add some more hide spots for him to feel more secure and heal up, he should start eating them I imagine.