The only criteria that I've seen that were consistent is that the home metaplane is either unreachable or unknown; that it is a spirit of some kind; and in those times where it's assensed, that there is a sense of 'wrong' about it, or corruption. Their behavior is /usually/ horrific or 'evil' in nature, sometimes for the purposes of feeding on the negative emotions.
Shedim, at this time the plane that the horrors came from is unknown, and they're spirits so they meet that criteria. I don't remember what they were described as in the astral, but for any critter that can (and does) manipulate the dead for it's enjoyment can't be good. I do however know they were described as addicted to the hate and fear they cause, so that meets the definition in my book.