[YES!!!!
One will kill at least part of the other and which one wins depends on the species involved.
Unless they are the exact same species they will kill at least parts of one of the corals. If you can move them or frag one that would be the best. Some people let them "fight it out" but unless you have a tank full I see no reason to do that!
I'm constantly having to frag my purple cap (grows to close to a hydnophora which is one of the deadliest) and another acro that always grwos into my purple rim cap! Thedownside of having stuff grow is you have to pay attention!]
