I seriously doubt there is an issue with the zoning. There are likely restrictions from the developer's perspective. To me, it sounds like this should not have qualified for an FHA or VA loan given the requirements for those platforms. You are placing the blame in the wrong area IMO. First the buyer should look in the mirror for someone to blame, then they should reach out to the lender as they never should have lent on the deal.
BTW, unless you have read every part of the PD and the subsequent amendments to the PD (which happens often), you cannot consider yourself fully informed as to the legally permissible uses. Central Florida municipalities are very familiar with this type of property and never would have allowed it to operate in this fashion if it were not legally permissible. It's not like some 3 unit landlord that gets away with some shenanigans, these are well-known property types with professional operators.