Im not sure if it would be a problem or not. Considering that the light from a projector is focused on the screen you probbly wont see too much reflections. I suppose they could be somewhat of a problem if you put the center channel behind the screen and have some reflections off the finish.
Keeping the grills on will keep reflections from coming off the front edge which is where it would be most noticable. However on my HG cherry's I notice reflections the most off the chamfered sides of the front
