This is something different.
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.