I just bought a used fretless that has a lined maple board and was strung with rounds. Maple is pretty hard, yet there was significant wear under the strings in spots, including discoloration due to hand oils getting into the rubbed-bare spots. I am having the fretboard sanded and an epoxy coat applied. So, rounds CAN do some damage, but if you like the sound, use a softer metal composition and not straight stainless steel.
Maple is a fairly hard wood, but the combination of it often being finished (poly scratches reasonably easily) and the ease with which is stains (being a light colored wood) means that it really needs to be either played with flats or given a very strong finishe (epoxy, etc_.