Is it permissible to count non-performing debts as Zakat after seeking the debtors' permission?

You are not permitted to recover your debt from debtors by counting it as zakat, even if they authorize you to do so.

The correct method is to pay zakat directly to the poor debtors without stipulating repayment of the debt. If they repay the debt of their own accord, then you may accept it; otherwise, you have fulfilled your zakat obligation.