You first created MP2 page, and you listed controllers as supported are you sure? because judging by what rockstar says it shouldn't be true..
Topic on User talk:Ricardinho
Just tried it with my controller and indeed it didn't work, it seems possible to emulate it using software like Pinnacle Game Profiler i haven't tested it though, so i don't know how well it works.
well.. so i think joystick support should be false