I’ve done the race a few times, 3x on a cross bike and last year on a short travel trail bike ( Santa Cruz Tallboy). There is a fair amount of pavement and flat-ish gravel between the major climbs that will reward a cross bike, but there’s more chunky gravel, especially on the downhills, that reward a mountain bike.
When I did it on the mtb, I felt fresher at the end since I wasn’t getting my body beaten up by the bumps so much on the downhills, and felt way more confident on those downhills. Also, having low mtb gearing was huge, especially at the end when you’re gassed.
All that said, I’ve never really raced it per se, just tried to survive and have fun. I believe the winners are riding xc rigs these days. If I had a xc hardtail that’s what I’d be riding this year—best mix of speed, climbing ability, and comfort.