There is 1 Dead Ghost to be found in The Hollows. They can be collected on any mission or during a patrol. Each Ghost can only be collected once per account.
Ghost 1[edit]
Head over and into the marked dome. It is blue and white with "CB" on it, for Clovis Brav
Head inside the dome. Deal with any of the Cabal that present a big challenge. Once inside head for the box that is opposite you on the ledge above the ground. Turn around and Double jump/Glide to the walkway above.
Look along the inside edge to find the Dead Ghost: