What you're looking at in the above gm stock photo is not a cooler, but a venturi style exhaust ejector. Right where the venturi is welded on, you can see the exhaust neck down to increase velocity & pressure. This induces ambient air into the venturi and increases the flow outwards.
They are probably using this device to decrease sooting on the rear quarter and tailgates of the vehicles by shooting the smoke farther away. However, as we've all learnt in school physics class; there's no such thing as a free lunch. Less sooting at the cost of a necked down exhaust... Not a winning proposition in my mind.
-Dan