The only "ADR" requirement on the rear bar is it should be full width.....even then, lots of people run narrower bars without issues. The rear of the vehicle doesn't have to meet the same sort of requirements as the front bar.
You shouldn't have any issue with the Atlas rear bar and carrier system from a compliance viewpoint.
I run a full width Uneek front bar and Atlas rear bar and carrier.....its a very good set up for the cost. I can carry the spare, two loaded Jerry cans and my hi-lift on the gate and everything is neatly stowed between the gate and the rear door of the JK....which actually makes it legal as the Jerry cans are NOT exposed at the rear of the vehicle (which is technically illegal for fuel). The only downside...the Atlas system is fairly heavy, just so you know.
Heres the Atlas loaded on mine.....