USRC is NASA sanctioned events.
RA requires cages that satisfy it's rules. NASA logbooks are accepted, but the cage must still be up to RA rules.
NASA accepts cages built to RA specs with an RA logbook (although there is some dissention among tech guys about that rule interpretation).
For new construction, RA rules (FIA, w/ a material allowance for DOM tubing) are more restrictive than NASA rules.
NASA rules do accept a FIA cage, but they also allow some different designs that would not be acceptable to RA (e.g. halo bars).
If you're building, build a FIA cage and get it logbooked with whoever you'll be racing the most (NASA/RA).