I know Oscars eat fish, but really that's the only one I know of. Not counting the fish that eat their young of course. But I know that the lfs sells the feeder fish to more than just oscar owners.
I find almost all fish eat fish that can fit in there mouths i have seen guppies and bettas eat small feeders.
But those feeders probly go to cichlids like Jacks, GT and even african cichlids.
Yes, I think feeders are too risky for introducing ich or some other disease because they are usually not maintained well. But, lots of people use them for arowanas, cichlids, amphibians, turtles, stingrays. I used them all the time for my monos (brackish fish). I bred them myself so they'd be healthy. Any large, predetorial fish.