I was there in June when tempatures were also in the high-30degrees Celcius. Even then they did fly. I was with a motorhome with the airco on, but stayed outside in the shade all the time. Just drink lots of water and you'll be fine. The residential area's around the track aren't really part of the touristic Las Vegas, you might even say it isn't the best part of town.
Was there in august a couple of years ago. Temperatures were 40-45 degrees Celcius, but in the late afternoon, beginning of the evening it is bearable... In the car with the airco running. Just go outside when the aircraft turn in for landing. It takes at least 400mm or better 500mm for good shots depending on the type. We stayed in a hotel in Las vegas itself, it's about a 25 minute drive (or so) to the racetrack.