I'm not so sure I need to return the emerald... he seems to make a point of hanging out with the two spotted cories (he'll follow, hide with, eat along side, and nudge them) and they're beginning to take to him. I'll keep watching to see if they reject or lose interest.
I may return him just to make sure my spotted cories have enough company and that the emerald do too (he was in a tank with 8 other emeralds).