ROLE_ATTRIBUTE_IS_DN_OPT is present and used by LdapExtLoginModule. However, if an AS7 configuration actually uses it, the following log is presented:

13:04:36,235 WARN [org.jboss.security.auth.spi.LdapExtLoginModule] (ip) Invalid or misspelled option: roleAttributeIsDN

It appears that it is not part of the ALL_VALID_OPTIONS array, and therefore is missed by the addValidOptions(ALL_VALID_OPTIONS); call in the initialize method.