I was far too close to this myself at a school in Ft Pierce, Florida in the late 90's and unfortunately illegality on one score often means illegality in other areas aswell.
Instructors were brought out on B Visas with promises of having them converted only to find after months of "Yes it's progressing very well" that no applications had even been made. At the same school students of British instrcutors were flying solo illegally because they didn't have the required sign-offs from an authorised instructor. At the same school aircraft were often flown beyond their 100 hour check by illegally using the 10 hour extension.
That school no longer exists and who knows, the leopard may have changed its spots however, if you wish to avoid taking any chances the person who oversaw all the above is still involved in flight training on the Florida east coast.