Yes, on a Rivendell you don't have to stay on paved roads- most of our rides include some really ROCKY backwoods gravel roads. Those are some of the prettiest routes. I presently have pretty wide tires on my Riv road bike (wanted them while I was getting my "sea legs"), but I'm planning to change to 25's or 28's soon. Must be well over 1000 miles so far over all kinds of roads (even across some fields in the tractor ruts) and no flats.
I love that Rivendells are made to handle pretty much whatever you set them up to.