Obito did the eye thing for Madara...Nah, it was more a coincidence. Madara already prepared Nagato and Zetsu, so, if Obito wouldn't have shown up, he probably would have sent Zetsu alone to influence Nagato in capturing the Bijuu and eventually reviving him.
And things like "Why did Obito arrive just in time to view Rin's death" don't count really, as this are typical plot coincidences that necessarily happen in every kind of fiction. If you start to question things with logic, you're getting nowhere.