And again I highly doubt that The Sage of the Six Paths is involved in any degree besides his legend. It wouldn't be him in the coffin because if it was kabuto could go through Madara. And it isnt the sage of the six paths reincarnated because he wouldn't have any reason to call him self madara, he would just call himself The Sage of the Six Paths which would be far more intimidating.
And it isnt impossible that Zetsu saved him, in fact within one of the latest manga he claims that he can become the land itself. And although he may not have been of the village that was at war with the leaf during the Obito incident, but ninjas are known to travel lol.
All I am saying is that Obito has the potential to be involved, it may not fall under him being "Tobi" exactly, but its not impossible.
I do think that the Madara is involved somehow, whether he is or is not Tobi is another matter.