There haven't been any studies done on the nutritional requirements of ball pythons, so even if freezing causes loss of some nutritional value, who knows if it's nutritional value that the snake requires.
All that said, I feed live, I've never fed f/t or pre-killed. I don't stun the prey, and I've fed off over 4000 live prey items without incidence or injury to any of my animals. I have over 40 ball pythons, all who feed live from hatchlings to adults.
I still stand by my opinion that feeding live purely for the entertainment value is the wrong reason to feed live.