The skinny. Dexos 2 is basically an oil spec that relates to additives to reduce friction vs low sulfides to prevent clogging of the DPF. My fav is Motul 8100 X-clean EFE. It meets Dexos 2 specs (GMC gets paid for every quantity of licensed Dexos sold) and it meets the ACEA C2 spec which has the lowest sulfide emissions that can block the DPF. If you want to stay compliant with warranty, you have to use a Dexos 2 oil from GMs current licensed list. This changes continually as not all oil manufacturers renew their contract with GM to put the Dexos 2 label on their oil....https://www.gmdexos.com/brands/dexos2/index.html
This is the most current offering from GM as to licensed manufacturers. It is out of date however as many of these are no longer offered.