I started my comment with As long as documentation is given that somebody is paying for editing an article. Besides, Sarah Stierch was an employee of WMF, not a plain contributor of Wikipedia.

As long as documentation is given that somebody is paying for editing an article, and of course if the contributed text respects NPOV (and the subject is considered worth to be present in Wikipedia), there is no problem at all. After all, you may use Wikipedia articles in a commercial work: it is sufficient that it is released under CC-BY-SA. So what's bad in being paid for writing?