UPDATE: RESOLVED
I asked over on Reddit and got a response from a gent who really helped out with this suggestion:
"RetroPie" >
"RetroPie Setup" >
"Configuration / Tools" >
"805: configedit" >
"Configure basic libretro emulator options" > At this point, you can either:
"Configure default options for all libretro emulators" OR
"Configure configure additional options for [EMULATOR NAME HERE]" In both cases ... go to
"Choose joypad order" and set which ever connected gamepads as player 1-4
I assigned defaults to all systems, then went in and specifically assigned the PS controller to PSX as 1 through 4. Restarted. Loaded up Tony Hawk 2 and presto, everything works perfectly (with the exception of wonky button maps but that's easily resolved) Thanks everyone for your input, I think* I have it all figured out now :) Hopefully if someone has this issue in the future they can dig up this thread and the solution.