Regular visitors to this forum know that you have bought into the system of "expert maintenance" by which "high-level" dance professionals are allowed to exploit clear conflicts of interest for financial gain.
Polished is absolutely correct to say that professionals should not be judging their own students when they are competing against other amateurs who are not.
Pro/am is such a racket that this discussion is meaningless in that context.
Terence has pointed out - more than once - that there are plenty of competent judges around. He doesn't say why they are not asked; I suspect that it's because they won't play the game.
Whether a judge would make a good coach - or vice versa - is irrelevant. A good argument can be made that the best judges would not be instructors because their judgment would be uncompromised by their own teaching methods.
In fact, it isn't at all necessary to have professional dancers as judges.

jj