It's kind of old news at this point, but I thought after rewatching this leg last night I'd post a few thoughts anyway. I'd been thinking that the heat was really bothering a few teams. Rachel struggled to walk the camels a mile, Rachel or Ashley (?) coughing and gasping in the cab, Dana's generally cranky mood, etc.
However, I just went and looked up the conditions in Dubai that day (November 29th, 2015). It was about as nice a day as you could expect in Dubai. High temperature was 82F/28C. Dew point temperatures were around 55F/13C, so it wasn't very humid either. Winds were around 5-10 mph so just a light breeze to help cool you a bit. So these were not conditions that should have caused any heat related problems. Another indicator was Matt wearing a flannel shirt over a t-shirt. However, I do think that walking in the sand would still be pretty hot with the sun reflecting off it and difficult with all the sand shifting around as you walk and getting into your shoes.
I figure that we're almost 2 weeks into the race at this point and at this point teams are pretty worn out, tired and run down. Throw in long plane flights that always tend to dehydrate me and pick up somebody's cold and I expect that nearly everyone is at less than their best now and will be for the rest of the race.