I've done this ride 3 times. The first two were the full Waffle distance and last year the Wafer. The course is designed, in general, to be ridden on road bikes. The routes are generally about 70% road so low rolling resistance is nice. The dirt sections are generally dirt roads, fire roads, double track and hard packed single track. There are also more than a few sections of sand which is often soft and deep especially if you are the 1,000th rider going through. And there are a few short, rocky sections sometimes slightly technical. The course changes year to year so not sure what the 2018 course will look like but will get a taste tomorrow on the 1st recon ride.
Myself, and most of my friends, run the Schwalbe Pro-One @ 28mm set up, of course, tubeless. This tire does extremely well on the road and is more than capable of handling the dirt sections. Last year I trained on the S-One @ 30mm (now G-One Speed). This tire also does well on the road but is a bit wider and has a bit of tread for those that are less comfortable on dirt - so a nice option. This year I'm training on the full G-One @ 35mm as I had a set lying around. It's nice having a bit more volume, especially for mostly dirt training rides, but they do ok on the road too. But I will be going back to the 28s again for the event itself.
https://www.facebook.com/events/417852031982429/