I suspect that Master Hugh may be actually a cultivar of the species R. macrophyla rather than a hybrid. J.D.A. Stainton's field notes may hold the answer. They are reposited at the Botany Library at the Natural History Museum in London.
Yes, I recall several references holding with the species R. macrophyla idea but I can't find the passages. Stainton's field notes don't appear to be available on-line. Looks like I'll just have to fly over to London and access the Botany Library at the Natural History Museum. Anyhow, today I planted 'Master Hugh' in semi shade in Nth Tasmania so by next summer should have an idea of it's tolerance of such situations.