Are percale cotton sheets cooler to sleep on than cotton sateen sheets?

yes Typically, yes. Take the thread count into consideration though. A higher thread count (say 500+) means a tighter weave, and therefore, less air can pass through the fabric. This will be smooth to the touch, but warmer. A lower thread count will have more "breathing room" and will keep you cooler. 300 still feels nice to the touch, but will not be as warm.