Aaron, think physics and entropy. While the IC metal temperature is lower than the surroundings, it will indeed absorb heat until it is the same temperature as ambient conditions. As soon as you start boosting and transfer heat from the compressed air, it turns into a thermal emitter. This is true even without the black-body coating.
Sitting in traffic will warm the rear face exposed to the header and engine block due primarily to radiant energy, but to some extent convection of heated air and conduction through hot brackets. Start moving and only radiant energy plays any part.
I wouldn't hesitate to get a black-body emitting coating as it would certainly improve heat transfer by RADIATING across a broader spectrum. It would probably help little to CONDUCT more heat to air flowing through the IC. That's a function of surface area and temperature differential.