My guess is that Gerhardt got in touch with Pound, who then introduced
him to Olson, Creeley, etc. Olson wrote a major poem addressed to
Gerhardt.  And Gerhardt shows up frequently in the Olson/Creeley
correspondence. Volume 4 of the correspondence (ed. by George
Butterick, Black Sparrow Press, 1982) includes a letter that Gerhardt
sent to Creeley and that he then forwarded to Olson.  There may be more
about Gerhardt in the Tom Clark biography of Olson, but my copy is at
home.  I believe that Creeley visited Gerhardt in Germany.  You might
write to Creeley, asking for his memories of Gerhardt.
Burt Hatlen