Surely. jura, the question is not about secrecy but whether they scratch each others backs as a result of being members of something that sounds like Enid Blyton's Secret Seven for big boys.
As a number of posters have shown there are groups doing each other favours everywhere from those favouring co-religionists or people of the same ethnic group, or local traders, or golf club members or rotarians, the list goes on and on.
The fact that one of these groups, doesn't publish its membership, although members are rarely secretive about their membership doesn't prove that their members do favours for each others on the quiet in a way the other groups don't do.
If someone recommends a good garage to me, I might take my business there once but if the work is done badly I won't go back, but if the work is done well, I really do not care if the garage was recommended because the garage owner and recommender are both masons, or play golf together, or just that someone found a good garage and shared the news.