It concerns me that ADP is charging you the garnishment amount since it is a deduction from gross wages no different than child support or even 401k or even still employee FICA and FWT.

I have never used an outside payroll provider but it would seem to me to teach payroll run the provider would collect from your bank account an amount equal to Gross Wage plus the weekly employer share on top. Since the garnishment is part of gross I would inspect my statements to ensure that ADP is not double dipping