From my reading of the WO Spec's I don't believe it is an issue of the DURABRIGHT not being 'capable' but more that the SCT adaptor is not supplied (I could be wrong however).
The real mystery is what is the 'gimmick' so-to-speak about the DURABRIGHT versus the Quartz?
They were both originally priced the same by WO but now the DURABRIGHT has come down and is slightly cheaper than the Quartz so it would be nice now what is the angle or thought behind the Durabright with a 15mm thick mirror otherwise why wouldn't WO simply stick with producing their Quartz diagonals?
As a point of pure speculation (inspired by the fitting) perhaps the thicker mirror is supposed to produce some sort of better output/optical performance with a refractor - pure guesswork here so please take this comment with more than a pinch of salt.