Can my son's great grandparents be granted visitation rights in NJ?

I am not sure whether you are asking about your great grandparents or grandparents. However, the quick answer is that a grandparent does not have any rights for visitation over the objection of a natural parent, especially when you state that the great grandparents were not involved in raising your son. The statute that states what a grandparents visitation rights might be is NJSA 9:2-7.1. What needs to be looked at is the relationship of the grandchild to the grandparent, the length of time that the child may have been lived with the grandparent the effect on the relationship that such visits would have with the child's parent or parents, any other evidence having to do with the child's best interests. Taking what you have written, it seems highly doubtful that the great grandparent would win.  The parent has a constitutional right to decide what is in the best interests of the child unless there are other factors involved. There must be a showing by the great grandparent or grandparent of a very strong relationship to the child if the parent objects.