I’ve never researched the Dos Passos-Faulkner relationship, personal and professional, at length. What I do know from my general biographical knowledge is that there was a strong professional respect between the authors.
When Dos Passos was awarded the Gold Medal for Fiction from the National Institute of Arts and Letters, Faulkner remarked of Dos, “Nobody deserved it more or had to wait for it longer.”
In this blog post at hottoddy.com, actor Clark Gable asks Faulkner to identify the best living writers. “Ernest Hemingway, Willa Cather, Thomas Mann, John Dos Passos, and myself.”