If Moses and Elijah came to chat with Jesus, I don’t see how saints couldn’t be the positive experience people have with “ghosts”
If God allows for the Devil and demons to do what they do I could see bad “ghosts” as these/could a human spirit be allowed to work for the other side? Seems plausible.
Then could some be from purgatory and have a different role on the earthly plain? Makes sense as well.