Yep, Stuart, FL used to be like that (maybe still is). No blue dashed ring or anything, just Class G but still had a tower. How the heck does that work? Well, from a reg standpoint, if you look into 91.126 (Operating on or in the vicinity of an airport in Class G airspace) under paragraph "d" it basically tells you that if there's a tower, you need to follow their directions. So in a way it's still controlled when that tower is operating.
Some airports like that have non-federal (private) control towers, and others might be awaiting appproval to become a Class D airport but don't have the operating volume yet.