The short answer is no. Although they should pay for Water Therapy. Check and see where the closest one to you is. You can go to a center where they have hot water tubs for the use of therapy and pain relief.
Getting Medicare to pay for even things it is supposed to pay by its own rules has been like gambling recently for many. I very much doubt they will pay for a hot tube. I understand how much better it makes you feel. I have chronic pain and being in hot water is the only time I feel pain free. Being weightless also allowes you to move more and exercise. So, I understand. You can find used hot tubes these days very cheap, sometimes even free. If you have someone handy around to install it that's a good option.
As an example of the gambling with Medicare. My mother has an Ostomy, she has no bladder. This requires some items that medicare pays for, supposedly automatically just as they do insulin for a diabetic. In this case it was Wafers, a small pad that is used where the pouch connects. They allow like 20 a month. My mother was using more like ten. Much to my mothers surprise, suddenly after years, they stopped paying. She had to appeal. Four Doctors wrote notes that it was a medical necessity, one doctor pointing out. " She will not be growing a new bladder back." To our surprise, two appeals later she was told it was time to go to court. We were shocked. Court...for wafers... The day of the "court trial" which is done over the phone. My mom recieved a call. " The judge decided in your favor, all back bills will be paid."
This process took 4 months and cost not only my Mom allot of grief but it cost Medicare the doctors and the taxpayers money and time.
I wish you the best.