As long as you have a Stable/Mature system w/ Pods, I am pretty sure they all end up eating frozen at one point. I have a pair of Blue Mandarins and a pair of Dragon Face Pipe fish in my tank and they all eat frozen food when I feed the tank. It took them a while to start eating frozen, but they all do now...
Very rare from what I have found. As mentioned, as long as you have a large enough tank, plenty of live rock, a productive refugium, and no competitors, they should do fine hunting for pods until they "learn" to eat prepared foods.
Haven't shared any pics of my tank in a while so I figured I'd add some more. I just recently picked up some of the amber/yellow film that you can put across your camera lens to reduce the amount of blue LED that comes through and it does a much better job showing what my tank actually looks like when I use my iphone for pictures now.