Out of all ski-related sports, ski jumping stands apart. Most disciplines rely to at least some degree on contact between skis and snow, but ski jumping is more about the interaction between skis and air. Snow contact is undesirable, because more contact means a shorter flight. The best jumpers barely touch the ground, alighting at the very end of their landing zone. This video gives a behind-the-scenes look at summertime training at the Utah Olympic Park.
Since the surface doesn't matter overmuch, it makes sense that summer ski jumping is a thing. As long as you have a moderately soft and slippery surface upon which to land, it works. The landing surface only really matters in the event of a crash, which happens rarely, but generally quite dramatically: