If you get one of the media modules that come with the back up camera kits, you could use one of the extra media input sources to add to a camera mounted into the car and it would show up on the screen. I don't have any experience with adding a baby camera, but I do have the back up camera, and do know you can add more inputs.
Current: '13 E92 M3 Euro Delivery
Wife's: E39 M5, E36 M3
Gone: E86 M Coupe; E30 M3