The UNS is a judgment call - not flagrant IMO, but depending on your supervisor, maybe a flag.
The low block is definitely a foul. RB is restricted to blocking below toward his adjacent sideline, and that's in the other direction.
In a 5 man game this has got to be the official who has coverage of the wing at the snap, or could be the wing official who picks up coverage of a man in motion.
In 7-man (not my strong point), I would think that it's the official who has the original coverage responsibility.