To me, it seems like IT would have to be significantly worse than the C's doctors thought in order for this report to be legit - like losing a month of the season to rehab versus a whole season to surgery. That seems unlikely that the two sides could have such disparate medical opinions.
That's why I'm leaning more towards this being a ploy to get more. Or at least it could be them trying to offload Shump in the deal, too.
It's probably more of a ploy, but if they're trying to move Shumpert, that's going to be a complete deal breaker.  The Celtics don't have any more salary to send out to match.  They're not sending out Tatum, which is what it takes to match that salary.
But it's possible that the Cavs doctors really feel that rehab just won't work for IT's hip, and that surgery is the only option.  That could easily be a six-month recovery time.  Early reports from IT's injury indicated that surgery was likely, and many were surprised when rehab was the way IT and the Celtics were going.  The Cavs doctor/training staff having a difference of opinion from the Celtics is still unlikely, but the possibility may be elevated in this case if IT's case was borderline as to what to do.
Like I have said numerous times, IT was very much at risk of having surgery before the trade happened so it is perfectly normal for an independent medical staff to determine that, yes, he might need surgery after all.
I think people really need to consider the ethical ramifications here for Cleveland's doctors and relax with the "ploy" talk.  That conclusion insinuates that that their staff is concocting a false diagnosis and/or proposing a more risky and serious treatment just to please Dan Gilbert.
I find that far more likely than the idea that the Celts doctors totally totally dropped the ball on IT and that they did it before a trade was even a discussion. 
That they just sorta took chances with his career AND that they didn't really communicate that to the Cavs.
You'd have to believe the Celts doctors are totally incompetent or that they're ok, but that Ainge is a liar.
I believe neither.  At worst I think the Celts doctors were optimistic and that Ainge gave the optimistic diagnosis to the Cavs. That said, the Cavs doctors and the Celts doctors knew it was optimistic, and that it could be worse than that.
The Cavs made a trade knowing full well the player had a significant injury. Now they're trying to say they didn't realize it was a significant injury even though they knew full well that it was and even though we sent the full report.
They think we're stupid.