I think that the traitor subplot could be a red herring.
I think it would be kinda odd to bring up a traitor subplot then have no real payoff/lasting effects of dealing with a real traitor.
How do we know that the villains didn't get their info from other methods
Say like hacking into UA's computer system or phone lines and using them to get the information that they want without the staff being aware of what's going on.
Another possibility is that it could be Koga impersonating one of the students at UA and getting the info that way.
Remember, that her quirk does allow her to impersonate someone if she takes the blood of someone.