This topic has taken a very odd turn after I first saw it a day ago.
The short version of the pox prob tho, it's a skin to skin thing. Just like chicken, small, and whatever other pox; so even legit massage is a problem. It's a serious concern for me and I'll also be pausing after finally getting a bit more active after these covid years.
The other thing is the sheets, towels, robes, slippers, table showers, and other things I'm forgetting. A customer could have it, no one notices, and leave some trace of it around an establishment. There's nothing you can do about that but I also think this maybe okay for mongers. The dirty massage places are usually the best for cleanliness because they're already dealing with fluids. They change and frequently clean sheets and towels, wash surfaces, inspect employees, and (quietly at least) inspect customers.
Short answer : it's a concern
Long answer : it'll probably be fine