Using QT 5.4.1 and QOpenGLWindow, it seems it's not possible to make the apple game center to show up.
Calling "[viewController presentViewController:mygcViewController animated:YES completion:nil];" doesn't bring any errors, but nothing shows up. Though it seems the game center window is "there", we can't see it, and inputs doesn't get to the qt window anymore.

It does work fine with QGLWidget (but Qt documentation suggest to not use it anymore)