Oscars will eat anything that fits in their mouths. So if the feeders look to big to go into their mouths, then the oscars might not be able to eat them.
Feeding feeders is not highly recommended because of all the dangers involved, and they are not highly nutritious for oscars. Feeding live feeders can also cause fish to become more aggressive, because you are teaching them to be predators. Feeders also carry diseases that can be passed onto your fish, so be very careful.
My oscar has only had a few fish (by accident) to eat in his life time, and he is as healthy as can be. Just buy the appropriate sized pellets of carnivore pellets, and I feed mine treats like frozen peas every now and then.