Obito was shocked, because Kabuto reviving Madara would mean Madara would be under his control, Obito unknowing Madara was too powerful to be controlled and could have disabled the jutsu at any given point. Obito's original strategy was to use Rinne Tensei at the exact moment the Juubi was revived so Madara would move there and become its jinchuriki.
He didn't want Madara to be revived, showing his disappointment when he figures out Kabuto has possession of Madara and when he was revived, and instead of himself, he wanted Sasuke to revive Madara with the use of Sasuke's Dojutsu.
Honestly I don't know, he believed in the Genjutsu but he doesn't have Tsukuyomi, that is why he was probably befriending Sasuke because he knew Sasuke had Tsukuyomi.