I play with this configuration in MaME and neo-Geo. Player 1 Picade Joystick and player 2 Xbox-360 controller.
In Retropie-setup install xboxdrv too
You must auto-config you re 2 controller (picade controller and xbox-360)
go here for add lines in your retroarch.cfg : http://www.open-consoles.com/t9401-presention-picade-mini-glooobule#115350 or for exemple :)