no doubt that certain forms of organisms thrive in harsh or toxic environments... some microbes eat oil for example. that said, being exposed to these things is not beneficial to humans in the short term (black mold in modern construction for example).

so whether something like is considered beneficial or harmful probably depends on the context... anything that thrives off gamma radiation would have to be very hardy indeed. the question would be, how dies it affect more 'traditional' life forms, like humans... and, is it natural, or another biowarfare lab creation? if the latter, the answer to the first question is probably settled.