From my perspective they're one way to find a job.
The way it works for me, the recruiter gets something like 10k if they get me a job, with the fee coming from where they found the job. So, offices would definitely prefer to not have to use a recruiter, but many of them have no choice if it's tough finding someone for the job.
I'm guessing it's something similar for NPs. It can't hurt to have recruiters looking for you, as they have every incentive to find you a job, but I wouldn't rely on them. Keep looking yourselves as much as you can, as you'd be a more attractive candidate if the job didn't have to shell out an extra fee for ya