So who is the author that Poe thought was the greatest American novelist?
It was William Gilmore Simms.
I was right about him being expunged. Online it says he was "purged" and it was "literary murder". It was easy to put two and two together on that one just based on the lack of two plantations of his wife's being listed among the haunted.
I found one fiction book of his available on the Gutenberg Project. The Blind Heart.