These durn fools are everywhere, and they vote.

I'd talk to him and see if I could help him with his hog problem.
I'd also gather up a little bit of information to show him, like the penalty for poisoning hogs.

It is the only non legal way to kill them, so I'd imagine (and hope) its quite pricey if he's caught.
If he proceeds, I'd have a ticked of neighbor because I wouldn't hesitate one second to call the authorities on him.
It ain't right, ethical, safe or legal, especially when it comes to you and your family you've got to keep an eye on him.