Bumping this as I have found some information that might be able to help those looking for this info. Once I get my truck in, I will try it out and report back:
Based on a few threads between 1550 and 2500 forums, the following 3 OEM parts would be needed to retrofit the vehicle to accept the OEM AUX camera(s) so long as you have the IOS Premium Infotainment System (if you have 'trailering apps', then you have it):
Swap out high-mount third brake light to part# 84699124 (w/ bed camera w/o Mirror camera -- ~$100)
Swap Trailer harness receptacle with part# 13530416 or 13526856 (~$75 - $95)
Add OEM Video Control Module 'VPM'
Open question: Does the IOS infotainment require an update or will it recognize the VPM & additional camera(s) once plugged in? Are pigtails for the VPM already prewired into the body harness?
My build for reference: 2022 2500HD SLE w/ Premium GMC Infotainment System and Trailering Apps. Unfortunately the dealer did not advise me to add the $250 bed camera option to ensure invisible trailer works.
Photo from another thread in the 1500 forums showing the pigtails hanging behind the rear bumper for the AUX camera input: