The issue isn't the good sam law, violation of a scope of practice, in otherwords, going beyond what you are licensed to do, is a misconduct/negligence, and yes people have been sued, the one I remember was in NC a SF medic who got sued by a chick he saved in a restaurant when she went into anaphalactic shock. He trached her to save her life, don't think she won, but he still ended up on trial.
Now do you really think the criminal that you helped into prison for a extend stay has anything better to do than sue you for permanently scaring him etc.
Now the above is for medical professionals, ie. EMT, RN's MD's etc.
BUT, here are 3 thing to consider
1. your safety
is the BG down, I mean you are safe around him as he no longer poses any danger, (BTW if he really is, EMS had better be really fast, or you skilled because the BG is most likely in a very bad way)
But it goes beyond that, is the scene safe, are his buddies gone, as soon as you lower you gun, are you going to be attacked, are you in danger of environmental stuff, standing in a street, it goes on, but the base question is, can you aid the BG safely?
2.
Legal, basic first aid is covered by good sam, however you end up the the BG claiming in court that somebody else was trying to rob, hurt, kill you, and he was just an innocent bystander, and you know that, why else would you have rendered medical aid after accidentally shot him
Then you have his family suing you for saving him, or if he dies, for killing him, and it might possibly be outside of castle law protections, since he died under your medical care....
3.
it's an equipment issue,
do you have BSI
what are you carrying to stop bleeding, what do you have for thoracic trauma, the list goes on.
and the BSI is a really big one, cause DOT can and does fine EMT $250,000 for touching a patient without gloves, and do you really want to bring a druggies Hebbie Geebies home to the wife and kids, hep C is nasty, AIDs suck, but so does TB and many many more.