Its a huge risk but Ive done it, just depends on your FRT. Thou just because they get along for some time doesnt mean that one day the FRT wont become curious or hungry! Theres also a risk depending on the ray size that your ray could drown your FRT.
Hey Tim.. I wouldnt risk it with your rays! you have some nice ones. I have 2 frt.. THey were both great for years.. Now I cant keep them with any fish. I lost a tigrinus and a silver aro to mine..
I know a few members who have done it with no problems and I also know a few who had problems it all depends on the personality of your FRT and how well you keep it fed.