This confusion about what no and what yes is, is caused mainly by a classical point of view on instruments.
If one skips that, and rely purely on the electronic conditions, with their own rules, then the division becomes quite clear.
With electronics, the source of the basic sound doesn't matter. One can modulate the sound. As long as the result sounds 'percussive', it should, in this case, be allowed to use in a Percussion Compo.