If you try to visit raterhub directly you receive the following message on an accounts.google page:
Ewok2 Rater Hub uses Google Accounts for Sign In.
Google is not affiliated with the contents of Ewok2 Rater Hub or its owners. If you sign in, Google will share your email address with Ewok2 Rater Hub, but not your password or any other personal information.
Ewok2 Rater Hub may use your email address to personalize your experience on their website.
This and other indications suggest It's most likely a company working for Google, imo. google has confirmed outsourcing the final quality control step, the human evaluation, to keep the indexes free of "sites that slip through".