Our experience is that if the kid is unusual enough to need labeling, then lots of people at school and elsewhere are already noticing he's unusual, so it's not like the label is going to change things much for the worse from a social point of view.
Once you are sure enough about the diagnosis to tell the child, it's also better for the child's self esteem to think that he's got interesting wiring than to think he's a terrible person who simply can't do what others can do but doesn't know why. The diagnosis can depersonalize the challenges in a useful way so the child and the whole family can grasp them and work on them without its being a problem of the "child being bad."
The other thing about the label is that if he's unusual enough to merit a label, he's also unusual enough to need the services that a label can bring at school. The label gives you the legally protected right to an education that is more appropriately focused on the particular child's needs. As long as that education is actually delivered appropriately (and this bears serious watching!)-- that seems to me an unqualified good. It has been this way in our experience with a 2E child.
As for the followup: tricky. Based on the very little I know of your DH, it might be easier to get him to go if it were couched as a parent education meeting with the child psych than if it were framed as a meeting with the adult psych about DH's own issues. He probably wouldn't like that. Right? It seems to me the child psych could probably tell you a great deal about how to manage the diagnosis as parents for the benefit of the child, information that could also help your DH come to terms more gracefully.
HTH,
DeeDee
