I have been on a couple short track race car pit crews and we always used Nitrogen in the tires. This was mainly because it expands less due to heat so we got more consistent tire pressures from the start of the race to the end.
That being said, I know I dont worry too much about pressure fluctuation in my TTs tires. If they where to get as hot as the race car tires, the gas in them would be the least of my concern. TT tires dont even come close to the heat or side loading that the race car tires endured.