In reply to JohnnyW:
Fresh snow on Arran this weekend but it was all unconsolidated fluffy stuff. When I crossed the peaks west of Glen Rosa (Cir Mhor etc) on Friday afternoon (prior to the new snow) there was next to nothing left from the winter, and I didn't need to go near any of the remaining patches.
Obviously that's not Rum, but as the hills are of a similar height and out to the west on the coast, I imagine conditions will be pretty similar.