If this is a seperate room, I don't see why just because it has a tub, the room needs to be called a "bathroom" and also NEED to have a crapper and sink.

Call it a physical therapy room, therefore not a 'bathroom' and not subject to the code requirements IMO.

Should be fine. Most codes are publicatly related, as far as accessibily and such, to the public. If there is a full bath in the house already, your covered. Much like every home is not required to be handicap accesble, its a private domain. All inspectors in this instance will understand the purpose, so just submit your permit, stating what your adding and why. Given that, the simple solution is to call the local plubming board, explain what you want to due, and see if you can get an answer without requiring a plan review consulataion. More than likely they would rather have a tub installed without, toilet and sink, depending on zoning laws,with fear of you later seperating the section of housing for renting purposes.