Back many years ago, I bought dead coral skeletons for decoration. Recently Ive made use of them by breaking them up and using them for LR rubble for frags etc. I also received a large Euphyllia skeleton (no remaining live tissue), so ive also broken that up. A remaining piece of SPS coral I had was broken up into rubble and now catches ALOT of detritus in one of my cannisters. You can use them, but as stated, tough, undesirable algae eventually settles on them, but if you dont mind that, go for it.