I have a non-Steam version of GTA V (PC), and I cannot get the Steam controller to work in GTA V. I can't get the Steam overlay to work in GTA V, either.
I've Google'd this for hours, and there are literally about half a dozen other people who have mentioned this and no working fixes.
I added GTA V as a non-Steam game. I launched Big Picture Mode (BPM) and updated the controller's firmware. I launched GTA V through BPM. Nothing.
Has anyone figured out how to get this to work? I'm extremely disappointed.