Is there a field in the Fraud API where a Paysafe account number can be passed?

Yes, you may send the information through the 'user_bank_account' field.
For reference, you can find all of our available fields here. Alternatively, if you have any other information that you would like to pass to SEON but isn't included in one of our default fields, then you can send the information using our ‘custom_fields’.