ibProArcade just checks the primary usergroup, so what you set in the Arcade-Permissions is only for the primary group.
I will check if the next update (ibPro 2.5.4) will also look the secondary usergroups
this will help me too as i would like my users in the secondary usergroup to have a bigger choice of games to play. does anyone know a workaround i can do for now so it checks the secondary usergroup too for permissions