Is it legal or ethical for a fighter to use his skills when in an altercation with someone not versed in those techniques? I was given to understand that the skills of an MMA fighter were not to be used on the street.

Every person who is trained in fighting should have the discipline to use that skill responsibly, and should only use it to protect themselves or others and with clear warning. That being said, the coaching staff at this gym lives out that idea and are passing it on to the students they teach.

Martial arts is a self-defense, that being said you have the right to defend yourself with the least amount of force necessary. I have not trained at this gym, but that's the first lesson you learn in every gym and every martial art I've ever studied.

im not that well rehearsed with what the law states when it comes to professional mma fighters restrictions / liabilities. I can only say that our professor wouldnt condone it. maybe research mma (ufc) professional/amateur licensed fighters restrictions, registrations? good luck