It would be politically controversial to do so, so I doubt it would ever happen. Definitely not from Obama, whom he exposed as a traitor to the very ideals that got him elected.
What oath? The only oath he was required to sign AFAIK is the Oath of Office: one defending the constitution, not the corrupt inbred military-industrial-complex that's grown up. His oath read:
"I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter. So help me God."
I don't know one way or another about a Medal, but this man has upheld his oath, and he did not allow reservation or evasion to deter him in it discharging it's duty. So help him.
Pardons are granted after someone has been found guilty. So far, Snowden has only been charged of treason and since he's not coming to the US to stand trial, a pardon is not applicable.
Maybe a new constitution amendment could be created to protect legitimate whistle blowers... since you can't count on politicians/Obama to do the right thing.
Pardons are often granted before someone is found guilty. The most famous pardon in US history, Ford's pardon of Nixon, was before he was formally charged with anything. The blanket pardon of Vietnam draft dodgers also wound up pardoning many people who had not yet been charged. A pardon of Snowden would not be improper procedure.
His accepting the pardon would be an admission that he performed the actions in question, but he admits that anyway.