It would depend on the size of the tank. In a large tank it is possible. The devils are much more aggressive and will easily take out an oscar in tight quarters but they tend to lose some of thier hype-aggressive behavior in large tanks. If you have a 180g or bigger than you could give it a try.
Who cares! This is the angel fish/discus forum!
Seriously, IMO, although I haven't kept oscars or red devils in many years, I think they would probably fight like hell.