Despite all the back and forth, I endorse the use of feeder fish, though not as the primary diet. I also agree that Hikari is by far the best staple food for these fish.
Isolate your feeders in a separate aquarium for several weeks before you feed them to your fish. You can isolate and remove any sick feeders. In the meantime, gutload your feeders. I heavily feed mine algae wafers, spirulina, and bloodworms. This technique is especially helpful at getting vegetable matter in the diet of picky carnivorous fish without resorting to starvation.
The ideal diet for oscars may be pellets, but there are fish out there that absolutely need live foods, especially other fish. To ensure healthy fish, make sure your feeders are healthy.