Search Firms serve two purposes for AD's.
First, the search firms are the ones that reach out first to guage interest, so that the AD knows who might be serious about the position. They help to quickly narrow down the field to realistic candidates.
Second, they give the AD cover if the hire goes bad
Feels like an intern for the AD could make those phone calls to gauge initial interest. I've never seen the blame for a shitty hire fall back on the search firm as opposed to the guy that made the actual hire. Imagine Wellman after the Bzz billboards went up saying, don't blame me, blame Thornburg Law Services.