I believe the club USAC is a member of ACCUS which is the FIA affiliated representative club in the United States. USAC have provided officials for FIA International (that are now FIA World) record attempts when staged in the USA - on the salt and on ovals. The timekeepers for Thrust 2 (Dave Petrali I recall) were under the auspices of USAC.
When Primetime ran the electric car in the Nevada in the USA they used SCCA officials, because USAC were already officiating at an endurance attempt in another State. As an FIA attempt organiser it is a matter of obtaining officials who are independent but are affiliated to the FIA.
As Dave Petrali timed the Thrust SSC bid USAC will probably have been involved in the last outright bid.
Of course for records not held under FIA rules there is no need for USAC or SCCA so they do not appear at SCTA (Speedweek) USFRA (World of Speed) or FIM (BUB) events.
Malcolm