I'm fairly certain the woofer grille is an integral part of the chassis and can't be easily removed.
The tweeter grille is, on the other hand, removable once you take the driver off of the chassis, but then there is this phase-plug sticker on the grille. I'm not sure if this sticker's absence is going to significantly impact performance (It will have an effect, the question is how much), but best leave it in place.
Will it look good without these grille? chances are probably not. They look kina unsuspecting as-is and since the woofer/tweeter is nothing to write home about, without any fancy texture or material on the diaphragm, removing the grille and revealing the deeply inset drivers probably won't help with the asthetics.