from my experiences with limas they aren't as aggressive as u'd think. mine is 15" and won't even eat feeder comets. but if u do have an unusually hungry one the armor will definitely help keep it from getting eaten. how big of a lima and how big of a raphael are we talking? if it's a real tiny raphael there's a possibility but if u make sure u'r lima never goes hungry i doubt much will happen especially if u have hiding places for your lil guy since u'll rarely see em come out.