There actually IS one risk with feeding f/t and that is not properly defrosting the prey and it still being frozen in the middle. That can cause the prey to rot in the belly of your snake, potentially leading to its death.
There are risks in both live and f/t and the keeper should be aware of all risks.
I only feed f/t to my kingsnake, but that's simply for convenience sake.
I breed my own rodents and have only fed live to all of my ball pythons, and have never offered them f/t or pre-killed. I've been feeding live for over three years and never experienced any life threatening injury. A nick or a scratch here or there, but nothing that endangered the life of any of my collection.