really depends on what the corals are, imho. I've found some things definitely don't like to be right next to mushrooms. I had to move around my colt coral until it was about 12 inches away from the shrooms before it was happy. It was clearly the shrooms that hacked it off.... I think they also affected a cabbage coral I used to have. haven't seen the shrooms affect polyps or xenia. Don't know about the leathers. I think you'll be able to tell if they're not happy.
This really comes down to experimentation. There are so many species out there with differing toxicities that it's nearly impossible to predict what will happen. I've seen mushrooms peacefully coexisting next to a carpet anemone (Stichodactyla mertensii), directly touching, for years. These two should be killing each other according to what most books tell you, but they don't. My only advice is to be cautious and watch them closely.
