That's the truth. Nearly every map I've worked on since discovering P9-P12 has not only used them but absolutely needed them (if its a major map).

No idea about the sound glitchiness, never seen it, and as long as you don't allow those players to be attacked, they won't get stuck trying to attack back.

Oh, I meant to say some. It was a typo.

I didn't have kerris attack me on accident...it was a scout, and my guy was just running by. I think I did change their race/owner to a valid combo [probably protoss/computer]. He even chased me for about two seconds.

Player 9 is capable of attacking.

Problem is that it is unreliable.

I've been playing around with that test map and I made 1 of P9's kerris to keep attacking. I also found out that if you burrow unburrow attack, then move away, it gets out of the frozen attack animation and follows your devouring one all over the place until you burrow. Also if you attack a building owned by it, it doesn't attack the devouring one I had near it, it doesn't change anything. When the map starts it attacks once then freezes unless you move away, then it follows you, again until you burrow.

I've managed also to get Hunter Killerss repeatedly attacking. I haven't finished testing but it seems to be that if you have 5-7 units around the one that unburrows, one of those units will continue attacking(very slowly). For Hunter Killers, 5 will leave one continually attacking(until you burrow). Devouring ones changed. Sometimes they worked, other times they didn't. I'll be testing this more, also with cloaked units just in case but I gotta sleep now.
Kerris seemed to be around 7 but I can't remember. When I start testing properly I will make a proper list of how to always get the same effects every time/