I don't think an "always on top" window would be above a full-screen app. It would be above a maximized window, but not a full-screen app.
If you can run your full screen app as a maximized window, then it would be possible. That is what I normally do when playing gamnes, except I have two monitors, so I can run other programs on the other monitor. But the full screen app has to be a maxmimzed window so I can move my mouse to the other screen.
If you can run your full screen app as a maximized window, then it would be possible. That is what I normally do when playing gamnes, except I have two monitors, so I can run other programs on the other monitor. But the full screen app has to be a maxmimzed window so I can move my mouse to the other screen.