I think on technicality he clearly violated sanctions.
It is all really gray, as you say. A regular person won't be prosecuted for staying in a hotel that's a front for the Cuban government to get hard currency and do money laundering, buying stuff from some similar place or going on a tour with another front company, the regular guy is not a public figure, he probably doesn't even knows about it, after all, he's just some guy on vacation and for the Feds, not worth the hassle.
But Hasan is public figure, that had to get a license (OFAC I believe) as part of the preparations for his trip, I don't know the content of the license, but I suspect is related to the hotel he was staying, the hotel chain is involved with GAESA, a front company of the Cuban government. As a public figure he's going to have eyes on him, waiting for him to slip.
However, I don't think he slipped or violated the license. Or if he did, was maybe through proxy, through the Code Pink and the other commie organizations that went to Cuba, these groups that are the actual target of this Fed business.
I think its those people that slipped or violated their license, they must have gotten one too, but we don't know the contents of said license neither the extend of what they got up to in Cuba. The Feds just want to press Hasan to see what they can extract from him so they have a better case against their real targets.
To his followers, they'll absolutely see him as a martyr. That's because they're deranged simps.
That's the funniest part of this thing. Hasan has been working very hard in turning from a political Twitch streamer into an actual political figure, that's why the suits, the interviews with prominent candidates, his campaign for the New York mayor Mandanigger, and such.
In my opinion, he wants nothing to do with his current audience, other than their money, they are actually a burden for him and his future prospects, see the post regarding his latest interview with a candidate, it was a disaster:
Related, a week ago, Hasan invited to his stream for an interview Nithya Raman, a DSA-affiliated LA city council member running for mayor against incumbent Karen Bass.
Hasan by talking with the Feds (he won't resist and he's also needlessly dropping names on stream), he's sinking his own ship. His cockroach nest of simps won't care but those guys do shit other than give him money, they are not running for seats, crafting policy, they are doing fuckall all day on the Internet, a good number of them don't even have jobs nor are in school, they are NEETs through and through.
But all the other political actors, the ones he's trying to court, will take notice of him talking to the Feds and when he, eventually, rats out his fellows (doesn't matter that the Feds are forcing you to give up the info, a rat is a rat), he'll be persona non-grata, destroying his efforts at becoming an influential political actor.
For him to get a deal, there must be things that he knows that the Feds can't find without his help.
Hasan has two options, fight or give in, and since he's a coward (he's squirming already), he'll give in. Like I said above Hasan is, probably, fine. Its what he's going to give up that will hurt the others (and hurt his prospects for growth beyond being some political streamer)
His lawyer also, probably, advised him to cooperate, no need to fight together with people that, given the nature of politics, especially 21st century politics, will sell you out in a heartbeat.