Thats fair, but the thing is that its YOUR PROBLEM(as a recruiter), not mine as a great "closed source" engineer
I know bunch of people who work on very cool and interesting problems/projects binded NDAs and have no problem on finding a new job if they want to. Hell Facebook, twitter, google are all closed source(mostly) so wouldnt you hire ex-Facebook engineer if he has no open source commitments?
Lets face it - its employees market, where companies compete for bright engineers. If you are saying that you only want open source commitments - thats fine, but you are betting on smaller market and missing some great talents. So you are more "lazy" recruiter, who dont want to look deeper, do facts check, test candidate etc. But again its your own problem, not mine.
Not every programmer is a rock star ninja. Most are mediocre. Some are pretty bad but know the theory and can play the resume game, pass the whiteboard test, etc. There are plenty of books and lots of advice that will teach you how to fake your way through a resume, cover letter, and interviews.
Worked at Google/Facebook/Twitter? Great. Odds are I can't afford to hire you. You're not the target of open-source filtering :)