You guys have to train with him. She has to live with him. Sounds like sensei has a problem. Talk to her some more. Talk to him. Put it flat out that husband is killing her dojo by holding everybody, himself, her, other students, back. Find out if he's killing more than that. If she cannot get a handle on this problem, hand sensei a card for a marriage counselor and go train elsewhere.
How does rank manifest itself in your dojo? This guy may be holding your ranks hostage, but he really cannot be holding your aikido hostage. Anything stopping you from just being a whole lot better than he is and just doing your best aikido? What happens when you go to a seminar (preferably in your dojo's association, if you have one) and other folk see that you are being sandbagged?
I don't want to get involved in their marriage at all. Not my place. I can only wish them the best with that and understand the situation they are both in.
As for training, it really is dictated by the guy's mood when we are there. He does not agree with the head instructor on most issues pertaining to technique and etiquette, so this can sometime make class feel stunted, even a bit awkward when the head instructor is there. A lot of sighing and eye rolling going on from off the mat towards him.
Other dojo and high level instructors are starting (just starting) to get a whiff of what is happening at this dojo. I'm not entirely sure what the outcome from that is. This person's absence at seminars has been noted by high ranked instructors that is. In the past we've all made light of it, or made excuses for him. But most recently it is harder to make the same excuse, 3-4 years in a row. They are getting the picture basically. But that also makes me nervous. I don't wish any negative outcome for the head instructor of this school.