Yea, pocillapora are cool till they're not. I used to find colonies growing in my skimmer and plumbing when I had a light in my sump on my old 120g tank. They don't really bug anything though, they're just taking up calcium/alkalinity for a coral you don't want. Some of them are very beautifully colored though. Nice trade for just chaeto though!
With the flame, don't worry about them not eating greens. I've never fed mine greens directly. The pellets I used to feed had algae in them, and I do see it graze on algae plenty. I'm surprised yours gets cleaned that quickly after introduction into the tank, but mine did the same too. My cleaner and flame angel have a much closer relationship than any of the other fishes.
If you're dosing for calcium/alkalinity, you should aim to dose them close to in equal parts, unless you're adding an acid somewhere which would suppress alkalinity disproportionately (i.e. dosing vinegar, etc.).