I was thinking about this. You're right that they do use temp agencies for most things, but the fact that these people had ANY badge probably indicates they were hired directly by Google. This was 2011, remember.
I have no clue who hired them, but I heard that the special badge was only ever used for that project and for a number of specific reasons that had more to do with lawyers than finances. (A bunch of us tailgated into that building once, but we didn't manage to stay past a minute or two.)
