Matheus,
While technically it's possible to have APs and controllers running different versions, it's *HIGHLY* discouraged and even not supported for anything short of temporary situations. Even then, it's normally only advised to have differences in WiNG versions that are VERY small (example: controller 5.9.1.0, AP 5.9.1.2, etc.)
There is no official testing that takes place in QA that attempts to verify compatibility between different versions of WiNG. For small version differences, it's usually possible, but again, you don't want to have a large difference like 5.9.1 and 5.9.2. The odds of there being a compatibility problem get larger the bigger the difference. Again, would only be for temporary situations where you will be upgrading all devices to the same version very soon.
It sounds like in your case, you are looking for a long term solution where you run one group of APs (650's) on 5.9.1.5 and the new 7632's on 5.9.2.x. If you made the changes necessary to allow this to happen, it would not be officially supported.
What you COULD do though is manually upgrade the 7632's to 5.9.2. After they adopt to the controller though, they won't be 'manageable' by the controller....meaning you cannot make any configuration changes to the APs using the controller. You'll simply see that they are online and the various stats from them. As far as I know, GTAC would not have an issue with this.