Shellcracker are not bluegill, they're redear sunfish; green sunfish also are not bluegill. Skinnybass says his bass are thin, i.e. empty, rather than not so empty. Although I'm sure they're eating something, just not enough of it. I would guess they're eating some combination of the few small bluegill they can find, small bass, and in the early spring, YOY crappie.
Certainly it wouldn't hurt anything to do a stomach inventory, but it's not going to correct the problem since not enough is getting into their stomachs.
