This is rather an odd question to ask, anybody would promote anything which is inline with what he or she created the a social media channel for..
Like if I was an influencer and very interested in gambling myself, then why not? I would promote gambling and casinos on my page so long as they pay me for it, the right question should be, are we going to accept offers even from unregistered casinos?
And to answer the question, I would say that it depends on the country where the influencer lives, like If I myself was an influencer and live here in my country, I don't mind accepting marketing offers from unregistered casinos because the government of this country careless about things like this, so long as the casino is not a scam, they can be marketed.
This is not to encourage any one to get into what is bad anyway.
Seriously? Would you do that knowing that bigger influencer you were, higher change you would have for legal consequences and change to get your social media accounts banned when they turn out to be huge scams? And you knowingly advertised them, even when they were unregulated.
There's a change to make money legal ways as an influencer that doesn't destroy your online presence, which would be something you should take care of in order to keep milking money out of it.
And it's not the country of the casino you should be worried about. If they are offering services to your fellow citizens and it would clash with your country's regulations, you might face charges for pushing those links.