I believe that Sargent's interwar performances of Hiawatha were given in a semi-staged format (rather like John Wilson's Broadway musicals at the Proms). This would probably make them more generally accessible than would conventional concert performances.
Incidentally, Longfellow is commemorated, with a bust, in Poet's Corner in Westminster Abbey. This seems rather strange since he was not British. (Yes, T S Eliot is also in Poet's Corner - but he did become a British citizen and, indeed, very English.)