Honestly I think it would be either a draw or go in Minato's favor. At the very least a draw as Minato is one of two people to be able to use the Death Reaper seal (since he invented it and taught it to Hiruzen).My question remains: What if they battled each other?
And plz, explain your oppinion... I'm not gonna flame this time (better mood)...
Since he has more chakra than an old Hiruzen, and used the death reaper seal on half of the 9-tails despite being almost out of chakra, we can safely assume that he could end it in a draw.
That being said if Oro goes to his true form then I don't see Minato being able to kill him as he can regenerate and his blood turns into a paralyzing gas.
But again this is only if he goes to his true form. He has obviously had this "true form" for a while now, but has never shown it in any battles except for the one against Sasuke. This is probably because he needs to be in his true form to steal bodies, which is what he was trying to do to Sasuke (and later either Sasuke or Itachi in their fight)
If he isn't in his true form I don't think Oro can beat Minato in a straight up fight. They are both highly intelligent, but Minato has FTG and is the best fuinjutsu user in the series, so that makes edos easier to fight as he can seal them, and if even Sai can seal an edo I'm pretty sure Minato can as well.
So here is how I see it going down.
Minato wins unless Oro is in his true form in which case it is a draw. You don't need to be holding the person like Hiruzen did to use the Death Reaper seal, you just need to be close, and if Oro thinks the battle is over (because of his true form's paralyzing gas) then he will be moving in for the kill.
Some things I would like everyone to remember. Oro's IWR is not Kabuto's. Oro controls the Edo ninjas and so limits their overall capabilities. He also has only shown two Edo ninjas. Also Minato has shown to be able to break control of summons just by touching a person and putting a seal on them. Obviously we have no idea if this would work on IWR ninjas but I'm sure Minato has some sealing jutsu to do the trick, considering that he marked Tobi for FTG and broke his control of the 9-tails all in one move.