That's only partially accurate. When it comes to keeping coral...whether it be hard coral like SPS or LPS or even soft corals, certain fish can't be kept with them because they will eat them or pick on them. Actually, there are many fish that will do that. On the other hand, there are a good number of very fine fish that are "reef safe" and pose no threat at all to coral. The best way to figure out which can be kept with coral and which can't is to get a good book and use that as a reference to chose the fish that would be safe to keep with coral.
Here's one that you can start with.....
http://www.amazon.com/PocketExpert-G...0068255&sr=1-8