The Cuban dogs do have tail a little higher in the air than what you normally see here but they still curl over the back. I've never heard of a tail without curl to be referred to as a "Cuban" tailset. Our standard says, "The tail is high-set and plumed with long, silky hair. It arcs forward over the back, but neither lies flat on the back nor is tightly curled......" A Havanese with a tail straight up in the air would never do good in the ring and shouldn't be put in there. There are way too many pet dogs in the ring now.
The only person I know who really understands the Cuban dogs is Kathy Steinig. She has seen them at the different stages. If the dog in question does have Cuban blood close up, then Kat could tell probably what the tail is going to do.
The "Cuban tail" is talked about occasionally over here on the West Coast. I don't think it really has any implication of being something that is found in Cuba. Instead, it is a nickname for the tail that goes up and hovers over the back or goes up almost straight with a tip that turns over the dog's back - like the photo you have linked.
We have had the Cuban tail in the show ring out here. I would venture to say that it is not desirable, but it is acceptable.