Downin3Green,
Here is a thread about a CA exercising command discretion in not allowing a non-flying UAL pilot to ride in the jumpseat of a UAL 757 in 2006, which suggests there is lingering animosity 20+ years later. (The thread gets interesting about half-way down, with discussion of a "jumpseat protection list"... (Nice euphemism, BTW. Potential CRM issues associated with such would take this thread too far afield.)
Why would UA pilot refuse to allow non flying United pilot to fly in jumpseat? [Archive] - FlyerTalk Forums
That aside, I think a diversion because of an issue arising between the pilot(s) flying and the cabin crew is exceedingly rare, and perhaps unique in the post 9/11 era; where, at least in the United States, bells and whistles are likely to sound at the TSA for any diversion of an inbound international flight. IMO, the CA may have more trouble with TSA about the diversion than with UAL management, depending on the reason he gave Miami Center for having to divert, and its correspondence to the truth.