@ apocalypz: only the Zetsu coat would modify his chakra signature of all the arguments you made and it would be a non-issue if Minato was a sensor, considering Ao and Karin were able to distinguish different chakra signatures within the same person (Danzou and Naruto respectively). Considering that, if he was a proper sensor, he WOULD know Tobi was Obito. Since he didn't, the logical thing to assume is that, if he senses chakra at all, he's very inexperienced on the matter.
PS: didn't know Tobimaru used T/S jutsu. Pretty big feat for a random falcon from Sunagakure.
Don't know why some of you think that Minato or Madara are stronger than Hashi. For me it's clear. Kishimoto has drawn Hashi as best Shinobi (not including sage, sons), in manga there are some moments which underline Hashiramas power.
And the vast majority of us know that, it just some people are such fanboys to their characters they're willing to deny reality in order to keep sucking their idol's cocks.