... But, even this doesn't really answer the question. "Traditional roofing materials" do not qualify while "solar roofing tiles and solar roofing shingles" do. But, is a non-producing tile/shingle part of the former or the latter? It is traditional in the sense that - particularly with the update - it is just metal roofing. But, it is designed specifically to work with the solar tiles and may, in some cases do things like covering/routing the cabling, so maybe it would, even if it is not a "solar electric collector."
It does seem, however, like the IRS does not recognize a notion of a "system" so I don't think one could solely rely on the idea that the pieces are all designed to be integrated in order to claim the full credit.