Any of the ones that I've talked to (either as they pass through town or when I'm down in California) have said they have their harps worked on - either a little bit or a whole lot. I admit the number isn't great but probably a dozen or so. It would be interesting to know what the percent of high end players would be and if the harps are literally OOB without any special prep by sponsoring companies like Hohner and Seydel.
]l'm just starting to customize my harps for over blows. I adjusted a Lee Oskar and a Manji M-20. I will be buying tools soon so I can replace and tune reeds on a harmonica.