Hi Kevin,For an eight bar intro you would normally leave the vocal line staff and use full bar rests. This actually makes it easier for the vocalist, and if you were making parts you would have to do this anyway. I would not try to hide the intro staff in this case.
Frenched usually refers to omitting whole empty systems and is used to make symphonic scores more compact. Just omitting a staff for a few bars is not generally thought of as Frenching, technically speaking.
Andrew
