I had an employer that did this on purpose, insisting because it worked so well for a time that it was the best way to do things for SEO. We owned almost 400 domains related to the business, and just had tons of comments and backlinking pushing juice the the handful of real websites.

I complained and explained it was only a matter of time before the whole thing fell through and got hit by an update or blacklist, but he didn't listen. I did at least redesign the main websites to be html5 with good metadata to mitigate it.

This is what happens when C-levels think it's still the dot-com era.