Nichole, we know this frustration.
Has your hubby tried histamine desensitization?
Was the DHE a drip in hospital at high doses for a few days, or a slow drip, administred IM at home over a long period of time?
Are you sure he was taken up to high enough doses of the verap/lithium - and in combo? (Between 960 - 1200mg verapamil and between 900 - 1200mg lithium?)
Has he been to a headache center?
I'm sure other headache centers have similar paperwork, but if he hasn't been to a headache center, please take a look at this paperwork. Being in CA, obviously going to Montefiore (located in the Bronx, NY) isn't a suggestion I'm making, I just want you to see the list of medications. Some are appropriate to only migraine, but I expect there are things on this list that your hubby has not tried - especially if he's never been under the care of a neuro from a specialized headache center.
Here's the link: Multimedia File Viewing and Clickable Links are available for Registered Members only!! You need to

or

Read down the page - you'll see the link to "Download the New Patient Questionnaire." It's a Word document.
Forget their headache diary - it's for migraines.
But I REALLY recommend you start keeping a "headache" diary. That's really a misnomer, because what you need to do is document EVERYTHING. Do this for one month, two if you can.
Have hubby keep track of everything when he's not with you and help him keep track of everything when you're together. But track the following:
Everything he eats and drinks (including water) and when
Everything he ingests, period, and when (including cigarettes or anything else)
Each attack and how long it lasts
Every medication he takes, when, and how much of it (including 02)
If possible, how much sleep he gets and when
Has he tried "busting" with RC Seeds or Psilocybin mushrooms? Those often work for chronics non-responsive to meds, and there is a lot of support available if he decides to give it a try. Feel free to PM me about it.
When at UCSF, did he see Dr. Goadsby? He does see new patients. Again, please PM me if you would like his e-mail address. See if he thinks there's any point in your hubby coming up there again. ????
Final question - did anyone bother ruling out Paroxysmal Hemicrania? It presents like clusters, but the attacks are shorter duration though far more frequent. It's a long shot, but he could be experiencing many attacks back-to-back that appear to be one attack. Indomethican, an NSAID, almost always works to prevent these types of attacks, and thus PH can be ruled out in about 9 days (3 days of taking one pill a day, 3 days of taking two pills a day, and 3 days of taking 3 pills a day. If attacks still happen, it isn't PH).
Do not give up hope!
Laurie