At its most basic form, the car will not meet the manufacturers standards. part of those standards being the ability to check you mirrors at ALL times. With or with engine running, battery connected, etc etc.
Now to be more specific about why you will have troubles. Remember back in the day when a bright light was caught on camera, it would leave a big white line from top to bottom of the screen from the glare. example
Well modern digital video cameras have a feature that prevents this. what this feature does, is it turns off the pixels that are deemed to be receiving too bright a light. Which is all well and good, but these turned off pixels leave a black spot on your screen as they are not receiving any data.
example
If the above was taken on a video camera rather a camera, the longer it faced the sun, the more pixels that would have shut down.
In order for the camera to know when a pixel is recieving light that is too bright, it compares it against the rest of the pixels in shot, if it is a certain level of brightness higher than the rest of the image, off it goes.
Now think, dark night, very little light out, car coming up behind you with its lights on, the bright light vs the darkness of the night. Almost all of you pixels will be black and you wont see the car coming behind you.
All of this being said, a GOOD camera would work, but you would need to spend the dollars (times two, one for each side) and after all the money is spent and gone, it's still illegal and you will get defected.
