Well, Shadow King is essentially a ghost, isn't he? And Xavier manages somehow.
Deadman isn't a regular ghost, though. He's cursed. No one can ever see or hear him because punishment from god, which includes psychics. (Mystics can work around it, the same way one mystic can channel the same power as Spectre and render his powers immune (Still left him vulnerable to a mini twister with some debris to the head from Jim..)