Ok I was assuming that he was pulling air from one source and exhausting into another. That assumption, means you can simply pull air in from one source (that is probably going to be cooler then inside the grow room anyways) and then pull the air through a carbon filter, through the fan, and through ducting to a completely different area. If that is accomplished, you will be able to stabilize the environment fairly well.

PS. I agree that although aircooled hoods help, just moving air between the plant and the light will keep it pretty cool as long as there is some flow in the room.