BTW, I've alternated between stainless and nickle rounds on my fretless basses, having pretty much stuck with DR Sunbeams for the last eight years or so. The D'Addario stainless (XLS series back in the day) I used on the first fretless did eventually cause me to replace the factory rosewood board with an ebony board, but it wasn't just the strings. I was over aggressive with periodically dressing the board and buffing it with a radius block and sandpaper to get rid of the small marks the strings left. I know that caused more wear than the strings did.
And I've had ebony boards since about '97 with only minimal marking. Yes, it does leave a mark. No, it doesn't dig gouges in the board. In my experience, most of the damage caused on fretless boards that is attributed to roundwound strings is really the bassist's technique. If you use only enough pressure to get the note, you control your vibrato and go along the string instead of bending it, and you keep the neck and the strings clean, you'll eliminate a lot of extra wear.
And Pino's had the fingerboard on the StingRay replace several times according to the book by Bacon and Day. He used VERY light strings. When he played with Paul Young in town a long time ago, one of my friends (IATSE member) was on the local crew. Because Larry was a bass player, when the roadie changed Pino's strings, he gave the old set to Larry. Larry brought them to the store the next day and we were amazed at how small the strings were, I think it was like a 35- 90 set.
John