i think it can be done successfully! I've driven 10's of thousands of miles with a jacuzzi in a bus. I do think however that the tub would need to be almost completely empty while in transit. Just having one or two 55 gallon drums of wvo on the roof of a bus causes very noticeable changes in the buses center of gravity. Not to mention that one huge problem with driving with a jacuzzi full of water is that the water likes to slosh a lot. Putting the jacuzzi up higher would only magnify this problem. You'd hate to clip a curb and send 300 gallons of water and a couple of bikini clad women off the roof onto the pavement.
this truck has prob 2000 gallons of water reasonably high off the ground.
Granted that truck has baffles in the tank to keep water from surging. You could also look around and find a jacuzzi that is realatively light. Some weigh 800 pounds, while others weigh 200 pounds. You do need a jacuzzi that is tough enough to handle the stresses put on it by water sloshing though. They really weren't made for that sort of force. some are better designed than others for this purpose.
the other issue is how to get the people up to the height jacuzzi and keep them from falling off the bus, even when stationary. ie: stairs a deck and a railing.
i once had a crazy idea to put my jacuzzi on giant hydraulic cylinders and raise it up through the roof. Having a jacuzzi on the roof would be a lovely way to attend the drive in movie theatre, or a sports game. ....i have a photo of that somewhere. I eventually after i wasted far too much tiem and money trying to make the gizmo safe i pulled the plug. (pun intended) the big problem i had was getting all the cylinders to go up evenly. In retrospect, i think that the lifting mechanism forks and all from a fork lift truck would perhaps be the way to go....with lockout safeties of coarse...but having it permanently mounted on the roof is prob a much safer and better idea than trying to raise it up there when it's full of water.