I've been playing a bare ebony board fretless for over 10 years, with rounds. Not my main breadwinner bass, but I play it a lot, even slap technique. It has marks and various artifacts of round wound string use evident on the fretboard. It's just really scratches and there's no depth of damage into the board itself that could affect playability. If you want the round wound sound, play them. For me, I want a fretless to sing, and flats only hum.
Ebony's a good candidate for a glassier, brighter tone because of its hardess and "ping" sort of resonance. The downside is that it's more brittle than other woods, but it seems that proper humidity, maintenance, and environment helps in preventing problems with that.