I am looking at 9/16" x 5" walnut to install over concrete in a kitchen. I plan to use a vapor barrier but do I also need any other type of underlayment? This is supposed to be a scratch resistant material but is there any type of engineered hardwood that is really scratch resistant? Also if a product like this is scratched what the options for repair.

I am not aware of any engineered wood flooring that is scratch resistant. Some brands I like are; BR-111, Khars, Homerwood, Lauzon, Mirage, & Armstrong.

I can see scratch resistant, but nothing is scratch proof. A better term used is "wear resistant".

http://www.andersonfloors.com/Hardwood/luster-lock.aspx