Yeah, it's the same vinyl used to make car wraps, advertisements, etc.
That grille goes to a very tiny opening in the radiator support which is almost right up against the radiator, so really there's not much chance of anything coming in from behind.
I detailed my engine this afternoon, and when I was done washing the whole inside of the engine compartment, there was only a couple drops behind the vinyl. If it were on the bottom grill that would be a concern, but it seems like it won't be a problem.
Although going down dirt roads, etc, could get stuff behind there... not really sure. I'm gonna keep an eye on it though.
(haha, and Dad walked up while I was cleaning my engine and was standing there watching for a good 5 minutes before he even noticed the grille block
)