To clarify:

It says Night battle 200% exp + vet rate 200%

The vet rate is in no way tied to the night battle. The exp is though. You get double exp for night battles today and double the chances of rolling for vets (can only be done while in harbor, thus cannot be tied to a game mode).

The +200% vet rate is just a little add on, and has nothing to do with night battle.