I am not 100% sure, BUT, I think most, if not all, of the cruise lines have a 3rd party company that takes care of their 'spas'. One company that has the concession, so to speak, on all the ships. I have had wonderful spa experiences on the Voyager and Disney's Wonder. And they were both operated by the same 'spa company'.
Just a little hint..... ask if they are going to have "sales".... sometimes, they run specials on the days the ship is in port. A 5pm treatment that is on sale is a treat after a long day in port.