Strictly true about the vents, but it won't necessarily decrease under-bonnet temperatures.
Air like water always flows downhill. Downhill in terms of air is from a high pressure area to a low pressure area. The area above the bonnet vent is low pressure and this pulls air out of the engine bay. This is not necessarily good. Air is pulled out of the engine bay, no cold air is pulled in through the same gap, and pulling the air out of the engine bay in this area interrupts the air flow as Nissan designed it in through the front/underside of the car.
Vents (unless designed specially and very precisely), as with raisers, will stifle the airflow efficiency and actually increase under-bonnet temps.
Agreed, also may pull hot air from the bottom of the engine/headers over the intake and raise intake temp, robbing bhp....