The thing about Fredo is that he really didn't think about anything beyond what was in front of him at the time.

So it's easy to say things like closing the deal fast meant getting Michael out of the way or that if Fredo was going to get a piece of the action meant that Michael would pushed out or killed, but I really don't think that Fredo considered this.

Either because he was stupid or blinded by greed and jealousy, I really believe that he just took Roth/Ola at their words and didn't consider the consequences of his actions.

That doesn't necessarily mean that he's not a traitor but I don't think that he was knowingly aiding in the assassination of his brother.