You can't pay for tuition with tax-free money and also take a tax-free withdrawal.
If the total tuition is less than or equal to the tax-free reimbursement, then you can't take a tax-free 529 withdrawal. Any withdrawal would be considered non-qualified.
If the tuition reimbursement is taxable, or the total tuition is more than tax-free reimbursement, then you can take a 529 withdrawal to cover the difference and it will be tax-free.
