We sprinkle some DE onto the sand during the summer months when we know it will be dry for a few days. Helps keep down flies and we've never had flea issues.
We also add DE to the shavings in the nest boxes.
We use play sand in the runs and love it. Dries out quickly, wicks water away from feces and dries it out faster, too. Never noticed it being much hotter than anything else in the summer. But our runs are in an area shaded by trees in the hottest part of the day.
The peeps seem to love dust baths, but they hate walking on the sand when it's clean and white
Doesn't take them long to get it to be NOT clean & white!