While you await an answer more tailored to your specific question, you may find this comment by /u/sunagainstgold which contrasts the emergence of American gothic literature in the northeast, postwar south, and Pacific northwest.

While I certainly would love a robust response to your question as posed, I think some degree of explanation as to why a Confederate ghost might be considered "spookier" than a Union one (or at least more of a go-to), can be extrapolated from that answer.