Very limber chinnies can sometimes scratch their noses with their back legs, but Leftie may not have figured this trick out yet. Also, missing the paw could throw off his balance and not allow him to use his back leg.
Maureen is missing her back leg (from an accident) and she still tries to use her stump to scratch itches. I think that it would interfere with her grooming a little, but her son and boyfriend groom the places she can't reach.
Hey, you were going to look at an ebony. Did you? Did you decide to keep Leftie your one and only?