I'll share my experiences with the nasty stuff. I had it bad (every rock was covered) in my old 55g tank. I did add a naso tang and he had it cleaned up within 2 months ( I sold the tang afterwards and have regretted it ever since)
I have dictyota in my 175g tank now too and the foxface does nibble at it occasionally but never puts a dent in it.
Interestingly, every once in a while large clumps of it disappears like magic and I have a suspicion (no proof though) that my abalone will come across it in his travels and will mow down all of it in his path. Worth a try because abalone can be fed nori when you run out of algae and they don't rearrange the frags and rock work like large snails do
(and they haven't come up with abalone police yet 
)