I have a Xmas tree rock. It's a rock encrusted with the SPS Porites. It has lots of Xmas tree worms living in it. I've read that there is a symbiotic relationship between the worm and the Porites.
Mine thrives up on top of my rock, baking under my T5's with pretty heavy flow. I've never had detectable ammonia, nitrites or nitrates. So I don't know how sensitive it is to those.
The only problem I have is that my pigmy angel likes to eat the Xmas tree's.
Here is a pic of when mine looked like before the angel ate most of the worms: