Bit of an anticlimactic update:
My wife got a text message from her son yesterday. the gist of it is, no need to worry about the dog, we gave it away. we still plan on having a talk with him to let him know that if by chance they get another dog in the future, that one won't be welcome here either. We will make sure he realizes, that it's nothing personal, we don't care whose dog it is, we don't want it at our house.
We were out of town this weekend for a family wedding, and my wife's youngest daughter went with us. She and her husband have two dogs, (along with two very sweet grandchildren). The subject of my wife's son visiting and bringing his dog came up. She kind of jokingly said well I'll make sure to leave our dogs at home when we come over. They live fairly close to us, about thirty minutes away, and they visit frequently, especially in the summer. She has never come over with any of her dogs, but just to make sure I did say "Please don't, we love seeing you and the kids, but we don't want any dogs at our house. (just playing it safe.................
As for her son getting rid of the dog, I'm actually a bit bothered by the fact that he obviously has been having problems with the dog, I don't think you just out of the blue decide to get rid of a pet. There must have been a final proverbial straw that broke the camels back. So he was willing to bring his problem to our house and expect us to put up with it just so he could save a few bucks.
My wife does agree with me fully on this, and we will be telling him very clearly not to do this again, even if it means he won't be visiting as much.