yes, but its just 3 wires and odds are that its not a USB port on the back of the deck, but wired into one of the plug connectors. same with the aux, probably not an actual mini-jack plug but just 3 other random looking wires in a harness.
that is why i would assume the plug for the stuff in the glove box did not fit on the nav deck and was not plugged in, but there is a chance that it is plugged in but was not activated. MMCS decks auto-sense connections to the deck and do not need the canbus for every little thing connected to them. canbus is only used for steering wheel controls, and backup camera auto switch. i do NOT know who made the navi in your Buick though.