Well yeah...
People counted it as Kakashi's arsenal so I don't see why it shouldn't count as Madara's now that he plucked it from Kakashi and using it himself.
It's just like Obito who wields Madara's(technically Izuna's) Rinnegan during debates with Jins.
Now Madara should be allowed to wield Obito's MS during debates.
Rinnegan/MS Madara