For my understanding there's no standard setup allowing to exclude VAT from Credit Check because "amount due" is coming from AR open items which includes VAT.
On the contrary "Open Order Amount" does not include VAT since an AR invoice does not exists yet.
In my opinion this makes sense if in your country you are going to pay VAT monthly on invoiced amount (aka VAT is payable even if you did not collect money from your customer), thus it consumes a portion of your company working capital.
Kind regards,
Carlo