It is against the law for him to hunt or trap these hogs and then SELL the meat. Violates state game laws, and well as the federal pure food and drug act, and the related state statutes on meat inspection.
I would get on the phone to the State Capital, and make several calls to find out exactly what agency is charge of enforcing these laws. Maybe it is the game department, maybe it is the consumer protection department. It will not take long to find out.
Once you find the department, tell them that you want to make an anonymous complaint. Give them your neighbor's name, address, and all of that good stuff.
Hopefully, someone from the State, wearing a badge, will show up on his doorstep, tell him they've got an anonymous complaint, and tell him that if they catch him doing it, its a felony and he'll be in jail in short order. This may put a big damper on things. Truth is, he could kill someone by selling them this meat.
And also tell the enforcement people that while they're out there on his place, to look at his slaughter pit. Believe me, they'll get tough with him.
Hope this works.
Mannyrock