I doubt there would be a problem with that combo as long as none of the fish were too small to be eaten and the tank was a proper size. Oscars are pretty passive as far as large cichlids go.
I have in the past. They got along great. The only issue I had was I couldn't feed my ray as much as I wanted to due to the fact that the Oscar would eat all the ray food before it hit the bottom. Other then that, it worked out good for me.
sound cool, my fish are still small enough where i could introduce a young wild oscar in the mix. i have tongs so getting food to the ray shouldn't be an issue.