You're to the point where that first thread trailed off and never got a reply.
They stated that it didn't work in the front-end (which is what you're seeing), but never responded if it worked within RetroArch, the actual emulator.
In a normal RetroPie setup, you configure the controller in ES, emulationstation, and then the buttons in RetroArch automatically map. Since ES isn't picking up how the input is configured out of the gate, it's worth checking to see if RA sees it either. To do that you'd want to connect a keyboard, configure that, and launch a game, then see if from within the menus of RA you can configure those buttons. If RA won't see the buttons that's when you're going to have to get into the weeds with compiling drivers or the like to get the inputs mapped to somewhere it knows to look.