We've been Labor Day week-end many times in the past. Alas, we haven't been able to the past couple of years due to school schedule changes for our family, but we always liked going during that time. Yes it is hot and as others said it depends on what you think it too hot. We don't mind it, we're from the northeast and love Disney in the summer, we really should live there!! LOL!!! Anyway, the only time we found crowded was Labor Day Saturday in the MK. It seems a lot of locals go that day. I would just avoid MK that day, maybe do Epcot, that's what we always did. Also, I would avoid DD Saturday night also, tons of locals are there, Pleasure Island and DQ are usually very crowded. I think you will enjoy Labor Day Week-end. Believe me I would be there too if my hubby (a teacher) and my son didn't have to start school early. We leave before labor day.
Hope this helps. Have a Wonderful Vacation!!