Try it but rabbits will gnaw on other hydrangeas as well. You might put a cage around it to keep them at bay.

The summer sun here is quite strong so I suggest making sure it gets shade starting around 11am (no afternoon sun). No evening sun either. Transplant it if it is getting more sun than that. My shrubs have handled 110+ temps in prior years with little leaf damage but they got zero afternoon/evening sun (only bright shade) and were already established by the time the 110s hit. Also, since it is a new shrub planted in the summer, give it even more shade with a chair/umbrella/etc and give it more water than in the Spring. I give mine 1g in the Spring; 1.5-2g in the summer per watering. During the daily 100s, I water 3 times a week, provided a finger inserted to s depth of 4" fels dry. Add 2-3" of mulch year around past the drip line to further help the plant. And watch for leaves browning from the edges inwards, an indication that they need more water. The round leaf spots can be ignored for now but are usually common issues due to overhead watering so, as a precaution, water the soil always, never the leaves. To remove ugly leaves, cut the petiole that connects the leaf to the stem. Hydrangeas get stressed when planted after late May here so continue giving it TLC and check it often in its first few summers. I have been looking for a TS/TTS locally. Where are you and where did you find yours?

One is supposed to be a darker pink than the other but not a true red. As usual and as you suspected, "Plant tolerates a range of soil pH, however, flower color will vary depending on whether soil is acid, neutral or alkaline." That is from the PW website. Thus, I would expect to have to amend with garden lime. https://www.provenwinners.com/plants/hydrangea/tuff-stuff-red-mountain-hydrangea-hydrangea-serrata

I'd honestly choose another plant and put the Hydrangea somewhere with afternoon shade. Shade cloth isn't ornamental, and full western sun in TN will make the plant(s) leaves look damaged. You could try one of the smaller Hydrangea paniculata types such as Bobo. They are white-flowered, turning pink late summer, but are long blooming and far more sun tolerant. I can grow them where they get more than 12 hours of sun here, but I haven't ever gardened as far south as TN. Or choose another type of shrub entirely that is more tolerant of hot sun.