Sports (and games, like chess) that involving competing directly against an opponent (basketball, football, tennis, etc.) are all about exploiting your opponent's weaknesses. If the opposing team has a slow PG, you exploit it. If you're playing tennis and your opponent has a terrible backhand, you exploit it. The exploitation of weakness is what makes these sports so great, in my opinion.
Injuries are no exception. But you have to draw a line somewhere, which is what you're asking, I guess. Intentionally trying to aggravate an injury doesn't seem quite right. But you can't go easy on a guy either. I say play your game and do what you always do and don't worry how it might affect the injured guy - let him deal with it. If the result is that you cause further strain to a bad elbow, so be it.