Lots of guys running true dual, catless exhausts on the 5.9 Dakotas. No reason why it can't be done on the Rams.

What I did was took the rear O2 sensor and left it plugged in. I then zip tied it to the frame rail so it's reading ambient air. Computer sees more oxygen than the upstream sensor, and says "wow, this cat is working really well!" and no CEL.

Other guys have had to use sims though. a lot of it depends on the year and the emissions package (federal vs cali)