Nothing in the manual says a COG, Vampire, or Ghost cannot be a psychic. In fact the Occultist class description says COGs rarely see the point but sometimes do. So how long can any of them maintain a Trance? Additionaly the lack of Con to add to Concentration checks makes the Vampire and Ghost which are listed as "the occult personified" at a serious disadvantage without having the Con modifier to add to it, that just seems contrary to itself to me.