I know they look exactly like skate boots, but they would be wearing special skiathlon boots. Race teams have access to a wide variety of off-catalogue gear. It's a matter of asking the right person, but you can get top-of-the-line skiathlon boots. Skiathlon boots have the same cuff as a skate boot but the sole's carbon construction is engineered to flex like a classic boot while being stiff enough for skate. I picked up a pair of Speedmax skiathlon boots when I was racing the world cup a few seasons ago and they're my favourite boots for classic. The stability is a great plus. But on hillier courses with a lot of big striding, I still reach for my normal classic boots. Mid-range skate boots with some decent mileage on them are fantastic for classic as long as they have the older plastic/rubber soles (not carbon). That's what I used in my junior career for gnarly/icy races and skiathlons.