I am aware that the 360 does not support the First Person mode in GTA V, I assume this is why there was no ST released for the XIM3.
I've been using my XIM3 on my Xbox One though, through the Windows 10 Xbox Streaming app. It works flawlessly. I could not be any more happier.
Although I wish the GTA V First Person ST could get ported over to the Xim 3 Manager. I don't see why it would be so much of an issue. The Xim3 does work on the Xbox One, so why not add a ST for an Xbox One Game(GTA V first person) to the Xim 3 manager.