You also run the risk of misaligned incentives. Ideally, you'd want to have industry professionals who know your industry and can evaluate employees properly, but aren't your competitors. Otherwise, they might try to poach your best candidates or recommend subpar ones.
There's also the misaligned financial incentive for headhunters in general. If they get paid every time you hire someone they recommend, it's in their best interest that you hire sooner rather than later to maximize their revenue/time spent.
How you brand or productize this service can bypass some of these risks. Just some concerns to think about.
An interesting thought: If you have a marketplace with resumes and ratings, the top-rated candidates will be approached much more frequently. This'll make them harder to hire and give them the power to negotiate better terms. Not a whole lot different than the rockstars who get job offers everywhere they apply, but a little more transparent.