Not really... I mean they can, but they don't actually need to. Radiation sustains them. No, radiation may heal them but doesn't make them immune to hunger. Like the guy from New Vegas where he hide from Nightkin, he eat radroaches to last, drink the drain water and "take care of his business" in corner. And then there is the guy from BOS quest where he steal military supply to feed the ferals. If the radiation sustains them, the feral wouldn't need to go out to attack people and fed on them