I could see how this could be viewed negatively....kinda like MMA fighting. While you see it as a vessel to build resilience and toughness, as well as a great form of exercise and stress relief, adcoms will probably already have a firm opinion about the sport, good or bad, which you probably won't be able to change. That, and the brain damage that is associated with such sports might make them think twice (not saying you have any).
On a side note, I listed Power Lifting as one of my most meaningful activities, and so far I've only gotten good responses in my interviews, and I think adcoms would have no reason to think poorly of extreme types of exercise. I'd say mention it, but you may want to spin doctor your responses to questions in your app and interviews such that it doesn't seem like you fight much, and accentuate the training and character-building aspects. I.E don't mention your W/L or anything having to do with the competition part of boxing.