You already have it and all of its components, so why not use it. GM may say that you're not
required to have one, but that's not the same thing as saying that such a hitch would not still be helpful. If the hitch has some form of sway control, integrated or external, it would still be worth while to use the hitch just for that regardless of the truck. You want all the help you can get to help prevent and help get you out of a sway event. When a trailer starts to sway, it will bring even the biggest of trucks down with it. This video was posted last year of a very capable truck towing a trailer. Just watch it and form your own opinion.
Not A Happy CamperManufacturer's infinite wisdom or not, I'd rather have some form of helping hands back than none.