Você pode usar regexp_substr para esse problema:
SELECT * FROM (
SELECT 'JACK' AS VALUE FROM DUAL
UNION
SELECT 'JOHN' AS VALUE FROM DUAL
UNION
SELECT 'BOB' AS VALUE FROM DUAL
)
WHERE VALUE NOT IN (SELECT regexp_substr('BOB,JOHN','[^,]+', 1, LEVEL) FROM dual CONNECT BY regexp_substr('BOB,JOHN', '[^,]+', 1, LEVEL) IS NOT NULL)
