Tough call. Trading for a guy who is out for 50 games and you don't know where his head is yet... kinda hard to decide. If he keeps up with the workouts, isn't a prick about everything, and comes back strong it's not a bad trade. But that's a long time to wait for potential payoff. If you think you can get yourself in a good position in your league's standings, and hold people off until he arrives to give you a boost, then maybe go for it.
I wouldn't do it, but I'm not an Oswalt fan. Honestly, given Manny's situation, I'm surprised you'd have to pay that much for him really.