Reading In search of Nella Larsen : a biography of the color line, by George Hutchinson (Cambridge, MA: Belknap Press of Harvard University Press, 2006). Van Vetchen figures very prominently in the book, as an important figure in her life: mentor, friend, sponsor. A look at his Wikipedia entry does not even mention her.
Van Vechten was a complex man, in many ways. One of his pursuits was photography. The Library of Congress has a collection of his photographic works: Creative Americans: Portraits by Carl Van Vechten at the Library of Congress features a searchable database of photographs taken by Van Vechten.
Another one is Carl Van Vechten's Portraits from the collection of the Beinecke Rare Book and Manuscript Library at Yale University features a searchable database of over 9,000 black and white prints.