Wow, I had this very same idea (get applied to jobs on one's behalf) like one week ago. Not from a startup point of view, but as job hunter. Actually I went as far as writing up my requirements and searching for some freelance recruiters near me.

(I already work for an awesome client, btw. Just wanted to experiment)

I had planned to keep my operation secret because if the employer discovered that I didn't personally apply, that could be an immediate discard reason.

Also, if you're already a good professional / job hunter, making sure the agent is equally good/consistent can be as demanding as doing the thing yourself in the first place.

Probably Mentat should keep those in mind - applying-on-behalf is a double-edged sword.