Easy on that one - all of those grilles are functional.
The vents on the top of the rear fenders and back bumper are for cooling the transaxle (the Corvette has the transmission located in the back unlike most vehicles) and for the rear brakes.
From the CFD images in that gallery, it looked more like they were routing the rear fender vent through to the taillight vent, presumably to cut a little drag (dumping some high pressure air into the low pressure wake). If they are actually going to the brakes and the transaxle, then they are more "functional" than functional. Rear brakes don't need cooling on a road car. In the unlikely event the transaxle needed cooling, you'd use an oil cooler, since blowing air over the case isn't going to do much. Regardless of whether these vents actually direct air anywhere, they are for looks more than anything else.