I feel like I can be of great assistance in clearing up some of this confusion.
FPW did indeed rip off "The Devil In Moccasains" when he wrote The Keep, but only in the creation of the character "Kaempffer The Limping Kanoodel", Glaeken/Glenn's comedy sidekick. All the other aspects of the novel; Molasar/Rasalom, The Keep itself, Poland and Nazis are entirely original creations by Wilson.
FPW was NOT influenced by LOTR, in fact he was Tolkien's ghostwriter during that project. Persistent rumours indicate that Tolkien's involvement in that project was restricted purely to the creation of Tom Bombadil, the rest of the novel attributable solely to Wilson.
Other pen-names frequently used by Wilson include Robert Ludlum, Jackie Chan, HP Lovecraft (the name under which Wilson also created the famously revolting condiment) and Ernest F. Spencer (for his stand up comedy routines).
I also have it on good authority (unfortunaltey I cannot reveal my source on this one) that Wilson Gave Rock 'n' Roll To Us.
I hope that cleared thigs up for everyone. :p