Hi there....blood sugars running that high will most definitely cause dizzy spells. Just before I was DX a Type1, when my sugars were running as high as you hubby's, I often had my world spinning. Not good. Neither are those blood sugar numbers.
You can lead a horse to water but.........you know the rest
Hubby HAS to take control of those outta control sugars if he doesn't want to seriously pay for it (yes, complications WILL occur if he doesn't get them controlled and soon. Stroke no necessarily being the worst of them.
As Warren suggested, get a few things checked out to rule out potential risks of other non-Diabetes related things. Might want to let him know, too, that if he ends up in emergency because of low or high blood sugars and he is a diagnosed Type1 Diabetic, the emergency doc has to report it. He could have his driver's licence taken away. That could still happen if his doctors don't believe he is being compliant with his diet and insulin regimen. Not fun.