I've heard they won't touch Dictyota, however, due to its invasiveness you may not want to introduce it into your tank. My tank has been invaded by every type of unwelcome and welcome algaes. My tank is too small to keep tangs, sigh. I have two types of Dictyota sp. in my tank, the larger and extremely invasive brown, and the smaller, beautiful irridecent blue that is far less invasive.
P.S. My reply to your post is in no way intended as a recommendation-Just every once in a while I have a powerful urge to play Devil's advocate.
Remember, be careful for what you wish.....
What about sargassum? I think it is also pretty invasive though. 
