Maybe the two following links to the official documentation can help you:

The GRANT statement does not list "ALTER ANY RULE SET" as a valid option http://download-uk.oracle.com/docs/c...ments_9013.htm

And according to this official documentation http://download.oracle.com/docs/cd/B...s.htm#BABCCCIE a special procedure is required to grant privileges to rule sets

(Note: I have never used rule sets, I simply looked them up in the official documentation, so I might be missing something here)