The alive checker has nothing at all whatsoever to do with google, it does not query google or any engine. It simply queries the site. If you wanted to find out if a pizza place was still in business would you call up a pharmacy near by and ask them or would you just phone the pizza place directly and ask? (phone the pizza place direct.)
Google can be up to 3 months behind on its crawl of a site, a lot can happen in that time. So the alive checker queries the site its self to see if the header check returns an alive status code or a dead one, in a nut shell.