I would think it's safe for the most part. How long have they been together, and do you have anything else in the tank with them?
Oscars can be funny. I've had them ravenously gobble up any excess fry that I throw in their tank, only to leave 1 particular fish, and buddy up with it, protecting it from the other fish in the tank. Then, one day, for reasons known only to them, they gobble it up. I think your loach is too big to be seen as food at the moment, and after they've been in the tank together for a few weeks, the oscar likely won't see it as food at all.