Not exactly. People in RVs accompanying riders on the ride are considered guests and must remit the appropriate fees. Moreover, the P2P support RVs have priority at ALL locations (including overnight, lunch, and break stop locations,) meaning your guest RV will have to wait until after all approved ride support RVs are parked at those locations.
NOTE: At Barstow, there is a very small parking area, subject to the above restrictions. At Ridgecrest and Bishop, we camp at the fairgrounds with adjacent RV parks, and Lake Diaz also has RV spaces, although Saturday night can sell out due to the Lone Pine Film Festival. Riders/guests with RVs must arrange their overnight reservations at each location.