I took a bold move this morning in the interest of getting official rather than opinionated information out about the admissibility of service dogs' being allowed to hike the AT through GSMNP.
Yes, I called the backcountry office and asked.

The ranger said that service dogs with their thruhikers are allowed. All we need is our documentation. I did not ask him what kind of documentation, from one's physician or from a vest selling business. I presumed the former.

I also asked about the $$$ involved. He said that we can get our permits online.

Fleur and I are grateful. It probably won't be this year, but whenever it is, I won't let those negative comments bother me as we prepare.