If you are using Routings and charging labor to work orders, then if the Work Order default for "Use Actual Cost in Enter Labor" is set to N then the labor and overhead rates in the Work Centers will be applied to the work orders.  If the default is set to Y then the employee rate as assigned in SM-G will be used.  If you are not using Routings and charging time to the work orders,  you can create a type L part number with an hourly labor and overhead cost and issue an appropriate quantity to the work order to apply labor and overhead cost.