Alternative to UNION

 I'm trying to create a view in Oracle that will be accessed by a vendor application. Apparently the vendor app does something weird when it access a view that uses a UNION or UNION ALL statement. Is there an alternate method to UNION that can give the same result? The query below is a simplified version. Any help would be appreciated.   -Thanks, Al Benvin

CREATE OR REPLACE VIEW COMBO_V AS
SELECT *
  FROM (SELECT ID
               FROM TABLE1)
  UNION ALL

            (SELECT ID
              FROM TABLE2)  ;