In my opinion, if you give an add-on you made to a few people, give it to everyone.
If you made to set your server out from the others then that's fine.
There shouldn't be any question here. If you make something, you have full ownership of the creative work. Nobody else has the right to distribute it.
Too bad that nobody actually licenses their add-ons which means "nobody else has the right to distribute it" won't work.