In my opinion most of these fish are hitting out of aggression. So they aren't taking it deep like bait, you'll get the occasional fish that does though and that's when it doesn't really matter if you set the hook.
One pointer I will add is when you are plunking there's nothing wrong with using a double hook set-up below your spin-n-glo. I usually run two 3/0 owner cutting points. Depending on the distance you are casting, determines how hard you set the hook. My favorite part is the bite, so I really let them have it, sometimes I'll hit them a couple of times. I haven't been down plunking the bar in quite sometime, I remember the last time I did it I was one of the few down there actually using bait, I'd rig a small pink prawn on with a toothpick and stretchy thread. This way you can't cast it off and the smolts and squawfish don't tear it off. Myself and two buddies used that set up a couple of years ago and we hooked 5 fish and landed 4. There were only three other fish caught that day out of 20 rods or so.
Keith