This is nothing new - they've been using humans for site rating and for search results evaluation for a long time. They also have manual ad quality raters. Leapforce is one of 2 or 3 agencies they go through.
They use human data to tweak, test and develop their algorithms. At one time, they were running HITs through mturk, which is about as low paying as it gets!
From the job description, this is NOT a site rater position. This project is apparently focusing on improving personalized search results, which is why they want active G+ users with web history enabled. Both of those are factors they use to customize your search results. (BTW, Web history is used even if you are not a logged-in Google user.)
The Google Play requirement surprises me a little.
PS - At least 2 versions of the site raters manual have been leaked. If you want to understand their viewpoint on spam and useful vs non-useful sites, it's a must-read... The original document, not somebody's summary of it.
