Don't Call a Cab

[localdriver]

Are private cars of guests staying at Disney allowed to use that back road the one with the security station on it to get to Magic Kingdom parking area?
In other words skipping that long main gate parking toll line, especially since resort guests just get waived through once they get to the toll booths?

I believe you are talking about Vista Way, which passes by the Campground, etc. Sure, you can use it. But there is no access to MK parking from that direction. If you go that way, you must turn right and go to 7 seas, turn left, go to the end past the Poly, turn left, go back out onto the main drag, turn around and came back in thru the toll plaza to get to parking. Doing so will most likely spend 10 min trying to save 5 min. It's best to just follow the signs to the theme park of choice, go thru the toll, show your resort card, and be done with it.