The most common question I get about the Ronde Ohop is whether I recommend a cross bike or a road bike. The answer is: Neither*. I recommend 28c tires. Beyond that it's personal preference.
*OK, here's a longer answer: The Ronde sits right in that sweet spot of terrain that neither really puts you at a disadvantage. Traditionally, the race has been won on a road bike. I think that has more, though, to do with the larger gearing available in the final sprint. The year Ronde was won on a cross bike was also the year it we had a mini-flood of the course and the Muur Mashel became nearly unridable as a result. In that year the smaller gears were a benefit.
So, I think the bike is personal preference. If you are getting ready for cross season or are a pure cross rider ride the cross bike. If you are a pure roadie ride the road bike. The course is hard, oh yes it's hard. But it's not a mountain bike race.
Which brings us right back to what's critical: if you roll anything smaller than a 25c tire you. will. pinch. flat. Heck, I roll 28's and you should too if they fit on your bike. Again, the dirt is hard and rough. It's bumpy. You don't need to be perfect; the trick is riding through the bad stuff and not trying to avoid every pothole. Push a low cadence, power gear and let the front end float. But no matter how good you are you'll hit something wrong and it'll be game over if you have 23c on. But 28 and you are golden!