The air dam is there to create a low pressure area below the engine compartment. This increases flow air through the radiator which increases cooling without having to resort to a larger radiator.
The loss of the air dam will increase pressure inside the engine compartment which will reduce air flow through the radiator, at high speed the engine may well overheat.
Air doesn't necessarily escape anyway possible, it can be quite happy stagnating. As ride height lowers and body shapes become more streamlined, and engine compartments more crowded getting air to flow where its needed gets to be a more complex and difficult problem. The designers of these things aren't guessing about flows, these vehicles get a lot of computational fluid dynamics run through the computer and a lot of real time flow instrumented in the wind tunnel. Of course one of the big goals they have is adequate cooling with minimum aero drag as this costs fuel against trying for maximum CAFE standards, so the factory solutions are looking at that as well so you may end up with adequate cooling against increased drag, for the average guy the drag is probably not a concern if they could even measure it.
Whether your set up will work, I don't know, just expect the unexpected.