Here is the code snippet for querying the list of users who have vacation rules enabled.

SELECT routingruleseo.rule_id,
       routingruleseo.MESSAGE_TYPE,
       routingruleseo.message_name,
       routingruleseo.begin_date,
       routingruleseo.end_date,
       routingruleseo.action,
       routingruleseo.role from_user,
       routingruleseo.action_argument to_user,
       itemtypeseo.display_name AS type_display,
       messageseo.display_name AS msg_display,
       messageseo.subject,
       lookupseo.meaning AS action_display,
       itemtypeseo.NAME,
       messageseo.TYPE,
       messageseo.NAME AS name1,
       lookupseo.lookup_type,
       lookupseo.lookup_code
  FROM apps.wf_routing_rules routingruleseo,
       apps.wf_item_types_vl itemtypeseo,
       apps.wf_messages_vl   messageseo,
       apps.wf_lookups       lookupseo
 WHERE routingruleseo.MESSAGE_TYPE = itemtypeseo.NAME(+)
   AND routingruleseo.MESSAGE_TYPE = messageseo.TYPE(+)
   AND routingruleseo.message_name = messageseo.NAME(+)
   AND routingruleseo.action = lookupseo.lookup_code
   AND lookupseo.lookup_type = 'WFSTD_ROUTING_ACTIONS'
 ORDER BY type_display, msg_display/*, begin_date*/