Some of them.
You can prove this by finding any random comment that has been around for awhile and searching for it in Google. It will appear in the search results.
Google will (naturally) prioritize posts to comments, but it will search comments if there is a far closer match than there is in posts.
Screenshot of Google search for this random comment:
Point 3 under "Scraping users’ profile", "Nothing about this transfers any rights from our users to us" seems to include the implicit understanding that SE already has the legal ability to allow access to that information.
does not come up with this random comment: