1.) Does Dom have Master strips on his arm?

2.) Why didn't RJ (and Dom if he had Master strips) have a master mode for his morph's?

1) No. He never really graduated. Master Mao sent him to find his path. I think it was because he was mischievous & had a bit of ADD.
2) RJ was all ready a Master when we met him. And his Sentai Counterpart debuted after the Gekirangers obtained their Super/Master Modes.