We will not know if it was just a knife, had some lighting, some wind, or a chrakra nullification seal.Sasuke Uchiha was using the same attack R'Kage was, that is why it negated. Minato wasn't using any lightning, just a knife..
We will not know if he would have been injured by that swing, but it looks clearly that it would because Killer Bee interrupted the attack.
If it was wind nature, A would have been injured in that moment.
PS: Minato is known to be a clever guy, do you think he would have attacked A's lightning armor with lighting? He would have deduced how to inflict damage to A before trying anything.
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