[jltsiren]

There is no green card category for being irreplaceable. PERM is for situations where it's difficult to find equally good US workers, with "equally good" left intentionally vague. The idea is that the employer is expected to argue convincingly that the foreign applicant is clearly the best person for the job. That's inherently subjective, but most things in immigration and the job market are.

Sometimes there is a shortage of domestic candidates with sufficient qualifications and experience in the general field. Sometimes the job is highly specialized, and nobody outside of a handful of internal candidates can possibly do it without extensive training. Sometimes the candidate was selected according to the established standards of a profession, and the job only exists for that particular person. And so on.

A fake application process is dishonest, regardless of whether it looks like a real job opportunity or is intentionally kept hidden. But if the process is open and you know in advance that no other candidate can possibly qualify, you are being not only dishonest but also impolite. Unrelated people may apply thinking it's a real job opportunity, wasting their time.