There can be custom group "you" call higher than superadmin.
But Gmod doesn't have any clue what other groups are, unless an addon tells it.
So, if you have Gmod default menus, that 'rely' on looking for the "superadmin" group, and turn off inheritance as in my suggestion to prevent superadmin restrictions from effecting your "higher" groups from being restricted (because anything that inherits superadmin will also inherit it's restrictions), then Gmod will not see them as superadmin access.
If you have gamemodes or other mods that look for those custom "higher" groups, then sure, they'll work.
Example.
If you have owner, and it doesn't inherit superadmin, owner won't be able to use the Gmod "Clean up all" command from the cleanup menu.