I understand at some point, there was an issue with Logitech or XBox one where these buttons were not working, but they definitely do now work with the latest Logitech firmware and XBox patch on XBox One. Check Project Cars II (pressing RSB from the main menu will take you directly to your profile, for example).
It would be extremely useful to have these buttons passed to the matching left and right stick buttons that work on a controller to enter Forzavista, vote on tracks in Multiplayer, or map to functions while driving, and it seems like this would be a reasonably simple fix to implement, as that functionality exists for stock controllers already, it’s just a matter of listening for those key codes from the G920.