Well, I have had a bit of a think now 
First, as your DH is diagnosed and under treatment, he is entitled to reasonable adjustments at work, isn't he? Many people with ADD find it very difficult to work in open plan offices, for example, because of noise or the feeling of being 'on show.' I also find that I am either in hyperfocus mode (very useful for research), or need a number of different tasks on the go that I can switch between quite often. (Other times I am sadly unmotivated at all.) I have also functioned much better in jobs where some admin support has been available - in my last one, I didn't have any such help, and didn't get it togeether to even submit my travel expenses
.
I think the usual way is to have an assessment from occupational health. Obviously it will help if he is clear on how his ADD pattern runs.
Second, how old are your DC? I know you said your DH doesn't like being a stay at home parent, but this changes as they get older. Although I was sometimes bored and frustrated, on the whole I enjoyed being a SAHM, and the reactive nature of the job suited me - though the housework was a dismal failure I must admit. It would mean that he would be in charge of much of his work pattern, and would have to try to set a good example of organisation to the kids. And hopefully your lives together would not be as stressed by rushing around as people who are both in paid work.
I did have a feeling that I wan't living up to my potential, but found fulfilment in voluntary work when the kids were older, which led onto paid work. It doesn't necessarily have to be The End
for him in that respect.
Do hope things work out for you both.