I tend to agree that arbitration will find Kaku was notified, but still looks a touch crappy on the org. The contract notification procedure should not be a unilateral email to a third party... Need to get acknowledgement from the player.
An option is by definition a unilateral contract, so there does not need to be any consent, acknowledgement or agreement. Further, the club is probably prohibited from contacting players directly about contract matters when the player is repped by an agent. Im sure there are probably MLS rules about this, if I had to guess.