I have been feeding live for a long time and only once has my snake been bitten by a live ASF rat It drew a tiny bit of blood but it healed immediately and there is no scar. If I didn't tell you, you would have no clue. The bite was my fault really. The snake I fed live to has been on F/T for a year. I ran out of frozen and only had live available. It was the only time she was offered live prey. She hasn't had live since though, but it is not because I am afraid, it is because I prefer frozen (they smell less and leave less of a mess (poop and pee in the enclosure)).
Is isn't bottom line dangerous, it is riskier if you do not know what you are doing. Making sure the prey is well fed before being fed off, and checking 10 minutes after the prey was offered. If things are fine but the prey is still alive, check again in another 10 minutes. If the prey is still alive, remove it. By that time its obvious that the snake is not hungry. If you have a glass enclosure, watching the whole process wouldn't do any harm either.