No, both husband and wife do not need to work to be able to sponsor a maid. I know several families who sponsor a maid and only husband works. The issue is immigration will use any excuse they want to deny a sponsorship request whenever they want. That is the problem when public authorities have all the discretion to decide one your request. Good luck, and if you are denied the sponsorship request (despite fulfilling all requirements) try to talk with the boss in immigration.