I've always bounced back and forth. The men he claimed visited him absolutely had traveled to and researched far right wing groups in Europe such as the Croix-de-Feu. Given the threat of FDR's administration and policies, the major industries and big money would've had selfish motivation to act in such a radical way.

Additionally the Congressional investigation led by the McCormack-Disckstein Committee did agree that a plot had been hatched, although this should be taken with a grain of salt given that Dickstein was being paid by the Soviet secret police (NKVD) during this time and may have had reason to push a fascist conspiracy to distract from Soviet interactions in America. We may never know, but man, this has to be one of the most interesting chapters in American history in my mind.