Engineers undercut each other all the time, implicitly, by going for the "do what you love and be paid for it!" nonsense companies throw, by feverishly working on unsupported open source projects for notoriety or to participate in the new culture of "github profile required or we won't consider you," and other ways I'm not listing here.

Those recruiters wouldn't be able to do what they do without at least some tacit approval or participation of labor.