I've worked with dozens of rays, they aren't picky about what they eat, whether it's on the bottom, swimming or floating on the top. In the wild, they do eat mainly bottom dwelling animals, but in captivity, they expand their horizons. You may have success with a very small ray like a yellow stingray, but only with a full grown cuttle.
I wouldn't do it. I had a yellow ray get a cleaner wrasse stuck in his mouth and it took both of them out. not good : (
Rays are incredible animals, but need a species specific tank like the cuttle.
Also if you do get a ray, make sure you dont use crushed coral as the substrate. We use pool filter sand (get it at great escape $8 for a 50 lb bag). They have VERY sensitive undersides and can get infected easily (same with sharks)