The rules state that when you add a mini to a group, the added mini may use what ever weapons are on the base card of the group. For example, the Z-22 has his weapon, and even shown by the model there is a rifle slung on his backpack.
Acording to the rules, when adding the officer to a unit, you don't add his white+black pistol, but you can use whatever weapons are in the unit, be it a rifle or trooper pistol.
Adepticon states that for Legion they are using WYSIWYG, and they made no distinction on "oh this is only for vehicles"
So how can an officer use the invisible rifle in his group while following that rule? I think it feels off that a tournament would have players break a core rule of the game just for sake of athsetics