At one time, USUA, EAA, ASC (Aero Sports Connection), and USHGA (US Hang Gliding Association) all had "Basic Flight Instructor" programs, to allow a BFI to legally instruct in a 2 seat "ultralight trainer". I think even AOPA might have been involved in the very early days. The instructor needed to be a BFI and the ultralight needed to be registered with the insurance.
EAA abandoned ULs early on, their ultralight registration program is likely vestigial. Later, when the Sport Pilot / LSA rule was passed (largely due to widespread abuse of the BFI program, so much for "self regulation"), the FAA eliminated the 2 seat ultralight training exemptions for everything except foot launched hang gliders and paragliders which USHGA (now USHPA) and ASC maintained.
USUA continued with the UL registration program which was required to get insurance through their affiliated broker, and provided a magazine which now appears to be defunct. There were also some shenanigans and disputes involving the USUA management around that time. It appears that insurance may still be available through USUA as per the link I posted above. When I had UL insurance through USUA around 10 years ago it was $300ish.