It is not a question of winter hardiness. It's a question of heat and humidity tolerance. If you are in an area where night time lows don't go much below seventy, you'll probably be wasting your time and money. Night time temps are THE issue that make gardening difficult in the south. Because our nights don't cool off (with the exception of upper south and higher elevatations, of course), plants never rest. They just keep growing and growing until they literally grow themselves to death.

I grew it for many years, under a White Pine, in acidic soil (red clay). The pine died after 40 years and the Gaultheria became exposed to afternoon sun. It slowly began to disappear and is now all gone, I think.
I believe that soil temperature has more effect on the plant than air temperature and humidity (dew point).
We often have soil tmperatures in the upper 70's and low 80's after a string of 100°+ days. Lots of plants wither and go dormant, when that happens.
In hindsight, I should have moved it, after having the tree removed, but I had Hepatica acutiloba and Asarum arifolium in that location and they are still doing fine.
In that location, I also lost Chimaphila maculata (Pipsissewa) and Chrysogonum virginianum (Green & Gold). Strangely, the Green & Gold had seeded into the neighbors lawn and is perfectly happy and vigorous (to his chagrin) in full afternoon sun! :>))
Rb