the reason for not purging the AQ$"_S" table is that this table contains purely static informations about your AQ configuration
These are no runtime data to purge!
>What is purge criteria to AQ$_<QUEUE_TABLE_NAME>_S when executing DBMS_AQADM.PURGE_QUEUE_TABLE to purge <QUEUE_TABLE_NAME>?
If you will setup a new AQ configuration these data will also be updated / recreated again.
>Can I use the DML delete to delete the records from _S table directly.
No, this makes no sense. You should never ever edit the AQ$ manually!