These contracted employees are working for other companies, not directly for Google. Their employer is Adecco or some other staffing firm (which I guess would vary by office).
It's very rare to see a large tech firm contract directly with an individual employee, and it would be incredibly rare to see it happen with a lower paid position. I've never seen it personally.
> If you're in HR at a bank on Wall Street, doing 'recruiting' - odds are you work for the company, not a contractor.
Quite a few of the people I've interacted with were contractors. You can sometimes tell from their email signature even if the email address is @bank.com.
Every company uses agencies for all sorts of things: recruiting, marketing etc..
But when you bring people in house, if they're working 'in' your company ... then almost universally they are 'employees'.
These are not 'security guards' or 'cleaners' who exist almost outside the scope of the work, they're very much within it.
If you're in HR at a bank on Wall Street, doing 'recruiting' - odds are you work for the company, not a contractor.