I dabble in the commodities busness....
Your buddy is not going to get in trouble here in AZ.
I have several friends with similar set-ups. No CDL required unless you are pulling above CDL weight for commercial purposes. If you put a dually pick-up bed on a full size tractor, and have "NOT FOR HIRE" signs plainly displayed, you will not be required to have a CDL.
My buddie's father had a heart attack and lost his cdl endorsement. He is retired, and used a Peterbuilt to pull his fith wheel. He got around the CDL requirement by putting a Dodge Dually bed on the back of his Pete, and having "not for hire" painted on both sides. I was with him when he was pulled over on the way to Glamis. They gave him a speeding ticket and sent him on his way. DPS never even mentioned anything about a CDL.