If someone is unemployed but married and files joint with their working spouse, will they be required to pay child support based on the joint income ?

Generally no. But the spouse's income will be examined for purposes of imputing some of the benefits to the person who should be paying. If "he" is unemployed and his wife is paying the bills, then his benefit might be the value of the rent, utilities and food. That can be imputed to him as "income." Another approach might be to calculate what the child needs based on the custodial parent's expenses.