Freehub has notches worn into it: is it OK?
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.