Spiritual mediumship such as contacting a ghost is considered perfectly legal by the Fellowship, they don't have a problem with a spellcaster contacting a ghost as long as they don't start raising them from their resting places or taking control of them.

Just keep in mind that for the most part ghosts in this universe are only a shade of a person, a memory of them raised by the circumstances around their death. They may have a semblance of personality, but they aren't full-on sentient beings just a shadow of the real thing. There are sentient spirits in the rp but ghosts are not.