Are you getting an Error or result count is zero? Please check date format in your table column END_DATE. Please also check if you are getting any error while running the query or by querying splunkd logs for DBX entries for checking query execution.
PS: I was able to pull the same using Oracle dummy HR table and your WHERE clause. Please find screenshots from db connection validation query and dbxquery.
| dbxquery connection=OracleConnection query="SELECT * FROM HR.EMPLOYEES E WHERE TO_DATE(E.HIRE_DATE,'DD/MM/YYYY') < TRUNC (SYSDATE)" maxrows=10 shortnames=t