It is certainly possible that Pound had a black nanny. J.J.
Wilhelm's invaluable "The American Roots of Ezra Pound" (Garland, 1985)
establishes that Ezra Weston, Pound's namesake and the man who mainly
raised his mother, had a whole staff of black workers, first at his hotel 
in Nyack. NY, and then at his boarding house on 47th Street between Fifth 
and Madison in Manhattan. Before Ezra (the poet, not the hotel-keeper) was
born, a black maid from the Weston staff (called Mary Beaton in
"Indiscretions") went to Hailey, Idaho, to prepare the way for the
newly-wed Homer and Isabel Pound. She disliked it so much that she returned
to New York before Homer and Isabel arrived. Apparently she later returned
to the Weston staff on E. 47th Street and might well have been there when 
Homer, Isabel and baby Ezra themselves returned in 1887. The whole story is
told in the first two chapters of Wilhelm's book. There are many references
to it in the Cantos and "Indiscretions".
 
Cheers.
Paul Montgomery
Lausanne, Switzerland