Quote:
It looks like site admins can access my hidden forum even though they're not group members and haven't been given permissions on it.


Thats normal. Since Admin is the highest ranking, it is impossible to create something that an admin cannot see. Normally a board of any size only has a few admins, and then people set to moderator to allow post control, but not board control. It's done the same way with this board, and any other software I have worked with as well.