It's not a con who is an artist felon, it's a con artist who is a felon. A con artist is "a person who tricks other people in order to get their money" according to search. It's someone who uses trickery is an artful manner to scam someone. Not someone who makes art and is a felon. Most con artist have worked on their scams to the point it's almost an art, which is a likely origin for the term.