They are a predatory fish and will eat whatever they can fit in their mouth. I've caught them on shad, bream and in the early spring my favorite big fish bait is a red horse sucker. I've caught them in areas that hold crappie in the spring so I'm sure they are feeding on them as well. But from 25 yrs of targeting them specifically and talking with some of the best stripe guides in the state, there is not another bait that outfishes gizzard shad on a consistent year round basis. Nothing even close.
Yes they use rainbows on Lanier and I'm sure you can could catch a fish or two on martin with them.