Where the stock "vents" are located should be an area of low pressure above the hood. Having vents there rather than ram air should allow the higher pressure air that's under the hood escape through the vents.I would like to see some independent third party testing like the Southwest Research Institute or similar company on these types of vents. I personally do not think they do much if anything other than aesthetics.
I run a set of S&B vents on my Rubicon that is more of a ram air vent and really see nothing of any significance in cooling the engine as I think that is more due to the engine design and cooling system than any engine bay passive heat venting.