If they weren't allies, how could Obito just think about capturing both the eight and nine-tails, and win a war in which he was challenging the 5 great nations?
His only weapons were the clones of the white Zetsu, which, regardless of their "copy ability", were such a big failure, and the Gedo statue, which was his trump card. In that way, Obito would stand against an Allied Shinobi Nation, who weren't weakened by the Edo Tensei reanimations, but obviously, he wasn't expecting that Kabuto would search for him and offer a helping hand, so I think that Obito was overestimated by Madara to think that he could manage a plan with such a great magnitude.
And as second thought, what were his plans for resurrecting Madara? Losing Nagato's 7th path, I'm curious how he would've managed this part of their plan. It's kind of luck for both Obito and Madara, that the events turned out as they are right now in the anime...