How did this work?

[SoulHunt3r]

Orochimaru stated that the 3rd summoning failed, not that Hiruzen prevented it. So no plothole, Oro just didn't know Minato's fate.

This ^^^

 

[Naruto Uzumaki Bijuu Sage]

People keep saying that the revival failed the final coffin because he was in the death god, But they forget the you have to preform the ritual first ( The one kabuto showed tobi), So it's obvious that oro has seen who ever was in the last coffin before he tried to summon him facing the 3rdhokage, Because again you preform the ritual, Summon the coffin the takes away the edo and the summon the edo when ever you need him.