The problems with judging different instruments are probably the same whatever the genre - I clearly remember being praised twice in classical singing exams for my wonderful breath control: this showed the examiner to be a non-singer/non-wind player or they'd have noticed asthmatic old me cheating all the way through. And then, examiners who are pianists are often thrown by how much trickier scales can be on, say, a clarinet. So, yes, it's easy to see that things could get even more problematic with umpteen varieties of pipes, concertinas, etc.