Having redesigned a hospital's recruitment process to use Facebook advertising for the more "blue collar" type jobs (porters, support workers, estates type jobs as well as nurses) I can really see this working.

We got ridiculous traction in the local area. We were reaching people who had never really thought of a career at their local hospital. But a hospital isn't just doctors.

Often with Facebook we didn't actually directly hit the candidate either. People's mum, uncle, brother or friend would find the advert and pass it on.

Facebook is already successful in recruitment. Only makes sense they really target this market and provide the business tools to do it