the bass will have no problem handling the shad and the bluegill. I manage several ponds with both and have no problems. what you can expect is a reduced bluegill population, if stocked at proper rates the bluegill will be healthy there will just be fewer BG in the pond.
It will help your effort greatly if you fertilize the pond. Its almost a requirement for the shad, without a green fertile pond you may have difficulty establishing a reproducing shad population
