It has been seen. I struggle to convince myself it is within a healthy norm but cannot atm provide scientific proof. It depends what this mass "around the waist" is. I doubt it is fat. It is probably intestines stretched with food being slowly digested, slower than the intake is. The worst case, it could be a bloat (gas), or a clog, or a parasite infestation but all these things spoil its appetite.
So to sum it up, I think there is too much food mass in his intestines but perhaps in a communal tank setting it is unavoidable with raphs. IDK.