Archie Moore referred to the middle knuckle as the aiming knuckle. If you look at the hands of just about any boxer, you'll notice that his middle and index knuckles are very large and prominent, the ring knuckle less so, and the outside knuckle practically non-existent. That is because it has most likely been pushed up to a point between where it was originally, and the wrist. That is what happens when you start landing punches, gloves or not, on that outside knuckle.
If you do it once you will, 100% guaranteed, re-think the idea of landing on the outside knuckles because it freaking hurts.
Most of the time when you land on the outside of the hand, it is because you aren't punching correctly to begin with. Waving the right hand, for example, as opposed to turning and driving it from the shoulder. This is why worhtwhile trainers dissuade boxers from "swinging" their punches.