Its fine (well to be more specific- legal) to have fake users/content on your privately owned website, but it will be fraud if they include those users and posts in their metrics provided to investors. In the US anyway.

If the owner of the site was in on it (adding fake users/content) and passed it off to investors as natural, I can see that as being fraudulent, but what if the owner legitimately wasn't in on it, as could easily be the case if the "fake" users/content were created by third parties for unrelated reasons and not detected by the owner? Indeed, the concept of using a throwaway per submission in certain circumstances is a well-known part of the culture, which is why I put "fake" in quotation marks -- accounts are only fake if someone erroneously assumes the ratio of humans:accounts would be anywhere near 1:1.

And if the latter is not fraud but legitimate usage of the site, then it seems like there could be a huge gray area of plausible deniability that the owner was simply using the site the same way that anyone else could (albeit with a streamlined interface).