L.L.
I think I adopted a dog from that same shelter about 5 years ago...the same type of dog also..although the dog we had adopted was NOT good with children or any other kind of animal and the shelter had not informed us of this, so we had to find out the hard way. We had to have him put to sleep the day we brought our newborn son home from the hospital because Spike (the dog) literally tried to snatch him from my arms and eat him for lunch. Luckily my son wasn't harmed.
Your priority needs to be your son, not the dog. Your husband is setting a bad example obviously. Have you asked him to please play nice with the dog so that your son will replicate the behavior?
I would be very careful with those kinds of dogs. Even though he seems tolerant of your son torturing him, they can snap at any minute. Dogs are animals, not people. So many seem to forget that when owning the family pet.
Lynsey