Sum Up values in a query based on other information
Here is a solution that uses analytics to prevent having to do two scans of mv_aeven.  It does require more CPU to save the disk access and is a bit more complex, so you will have to weigh it accordingly.

SELECT * FROM
(
  SELECT a.eventnum, sum(a.num_cust), sum(a.out_minutes), a.off_dts, max(a.restore_dts)
     , a.cause, a.feeder, a.DEV_NAME
  FROM mv_outage_duration a
  WHERE a.DEV_NAME = 'T007F12127'
  GROUP BY a.eventnum, a.off_dts, a.cause, a.feeder, a.DEV_NAME
) a
INNER JOIN 
  (
  SELECT Num_1, xpers, weather_code, completion_remarks FROM 
     (
     SELECT Num_1, xpers, weather_code, completion_remarks, rev_num
        , max(rev_num) OVER (PARTITION BY Num_1) max_rev
     FROM mv_aeven
     )
  WHERE rev_num = max_rev
  ) d
ON d.Num_1 = a.eventnum;


SQL Fiddle (Includes column type definitions).