How does Kabuto have 6 Edo Jinchūrikis when the bijū are sealed inside Gedō Mazō? Anyway, Kabuto's only problem is that he's likely oblivious to the fact that there is a means of defying the Jutsu, and that Madara knows these seals. Giving Madara free will wouldn't really be wise, particularly if he's fighting someone like Obito who Madara is sure to pick as his ally. Simultaneously controlling all those summons would prove very difficult indeed. Kabuto's best bet would be to send out waves of summons, perhaps 2 or 3 at a time in order to tire his opponent.