ive seen plenty of ppl with pollys as tankmates. ide give the polly somewere to hide if possible but its a case of putting it and and keeping an eye on it.
an aggressive polly may bits a ray, an aggressive ray may cloak a polly.
before anyone else jumps in, you tank sounds like its pritty much over stocked with 3 rays and 2 aro in a 180. your upgrading yer?
the tank is to small for 1 silver aro in the long run never mind 2 and 3 rays.