I have a PHP forum (private, special topics) on a domain I own.

Yes, it is possible to have special groups and subgroups that only have permissions for people that are given administrative permission to be on certain groups - sample groups can include board members of a club for discussion of club related issues; special committee chats such as rescue fund raiser discussion groups; genetics discussion; sections of the forum where only members of the club can chat, and sections where nonmembers can ask everyone else how to train a livestock guardian dog (for example) or solve a problem, and so on. Special permissions can be given to guest speakers, such as someone who might discuss wolf conservation among members who ask to join a private discussion group on the one board after being polled.

People with special permissions automatically see the -hidden- topics when they log on. Everyone else just sees the generic areas.

This board, Pet Talk, for example may have special subjects that only Moderators can see (this is most common), and special subjects that only certain other groups see.

This is posted with due respect to Karen and other admins. I think they have every right to administer as they see fit and fits their resources.
I think they are very generous with their time!

The only issue I'd have with special request groups on my forums is that it is more work for the admin(s). So the value of the special group and their "group" & "permissions" depend on priorities and resources available.