I'm also inclined to believe that the scroll Suigetsu found has to do with Oro's experiments, involving Hashirama and Madara ... and perhaps Zetsu is one of those experiments.. or when Oro first joined Akatsuki Zetsu came there with him and used the DNA to create Tobi... It's very reasonable to assume that if Oro was experimenting with the 1st's DNA then it's safe to assume that he tried to get Uchiha DNA and experiment with it as well, though as stated with Yamato, none, or only one survived...
For me, Tobi IS by all means a Zetsu clone .. confirmed indirectly in the manga more than once.. fighting Fu and Torune (ripped his arm off (White Zetsu)), fighting Minato (flashback when Naruto was told by his Mom) the rasengan tore him up and showed the white Zetsu blobs melting (even showed it in the Anime, which I dont think takes too many artistic liberties when making).
Now I say the scroll is information over a jutsu only because if it was a badass jutsu that could change the tides of a war, why wouldn't he have used it when needed (when Itachi was sealing him in the sword) ?! just a thought there ... so yeah .. leads me to think it's information ...
here's a link to my thread about Tobi being a Zetsu clone.. if you wanna read it...
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