If there is a subset of people who can't be vaccinated that constitutes a legally protected class, that would be news to me. Wouldn't any such subset be small enough to admit to the promotion manually?
Absolutely anybody outside of the US, UK, UAE and Israel cannot really expect to be vaccinated at the moment. There are also any number of health conditions (MS is an example I'm aware of) where you definitely will not get a vaccine. I imagine that HIV might also be a no-go for vaccines. Is Hyatt going to get into the business of double-checking your HIV status to manually add you to a promo? Of course not...
I imagine that the US legal system offers little protection for non-Americans as a minority class, but a promo that excludes 90-95% of the world's population could easily be sued anywhere that Hyatt has a hotel.