Freehub has notches worn into it: is it OK? I bought a pair of second-hand wheels, and after removing cassette noticed these notches on the freehub. Is the freehub still in OK condition?
The bumps on the freehub splines are caused by steel cogs on the cassette digging into the softer aluminum metal on the freehub.

You can use a file and file down the ridges, once, maybe twice without affecting performance too much, but eventually you will want to purchase a new freehub. 

Depending on your needs, you can purchase a steel freehub and this issue shouldn't be a problem.