by "dead" do you mean dead and dry decorative coral you find in the LFS
sitting on a shelf? Or do you mean, dead and still a little damp cause it used to be a live coral a few days ago?
if it's the dead and dry decorative coral then certainly add it without worry (as long as it's clean) and eventually coraline and other bits will grow on it just as if you were to add any other base rock.
If its the dead wet coral (recently dead) then there might be some room for caution only because the decaying coral will raise the ammonia in your tank slightly (depending on the size of the coral and the amount of denitrifying bacteria in your tank) I may be wrong on this last part but I have also heard that some corals may release toxins when decaying (I may be confusing anenomes here, pardon me if I'm remembering wrong).