Not Gresham's Law per se, as it is specific of money. But what you're describing is essentially a form of adverse selection (see Akerlof's "Market for Lemons").

Not Gresham's Law per se, as it is specific of money. But what you're describing is essentially a form of adverse selection (see Akerlof's "Market for Lemons"). If employers lower their wage offers below the reservation wage of graduates from prestigious schools, then they would leave the "undifferentiated" job market. But there might be more to it. Graduates from better schools might still accept job offers if they could hope to get a raise once their true value is discovered.