"Insider" may not have been the best choice to describe those events. The true "insider" events would have been things like Indian Neck, which was (and still is) by invitation only.

Fox Hollow in particular was started by Bob and Evelyne Beers as a way to gather their widespread musical friends in one place for a weekend. Many of those friends were working folksingers and musicians, but others were rarely seen and heard outside of their own communities, except perhaps on a Folkways or Folk Legacy LP.

Fox Hollow, and the camps at Sweets Mill on the West Coast, were the gatherings of the tribes, where people from different communities could share their music and catch up with one another. The social aspect was at least as important as anything that happened on a formal stage. And performers were a lot more accessible to the audiences than at bigger festivals like Newport and Philadelphia.