When I posted last Friday about a mockup rear bumper for the C7 that would accommodate round taillights, there were a few posters who thought that the taillight vents on the actual C7 were fake. I'd like to clarify that here.
The taillight vents are real and, along with the rear diffuser, let out the air taken in by the fender vents for cooling the transmission and diff. Whether the fender vents on a C7 are real or not depends on that C7's transmission and if it has the Z51 Package.
While I don't want to sound like I'm soaking up all the hype that GM's made over the car, it looks to me as though most every feature of the car's exterior and interior is designed the way it is for a reason. I don't think it seems unreasonable, at first glance, to assume that the vents have a purpose and aren't faux plastic bits to make it look aggressive or flashy (see: every new beigemobile).