As long as you seperate ads clearly from the site content and maybe give them a rel="nofollow" attribute, there should never be negative consequences.
Paying someone for low quality content around links to increase search engine rankings lowers the quality of the overall web for everyone.
Google does a lot of questionable stuff and I personally don't like the power they weild over the web. However, in this particular instance, I can't see anything wrong with this policy.