I use this regularly:

COL TSPACE FORMAT A25 HEADING "Tablespace"
COL STAT FORMAT A12 HEADING " Status"
COL TIM FORMAT A18 HEADING "Last Hot-backup|StartTime"

SET LINESIZE 100
SET PAGESIZE 20

SELECT
A.TABLESPACE_NAME TSPACE
,DECODE(B.STATUS
,'ACTIVE','** BACKUP **'
,'NOT ACTIVE',' NORMAL'
) STAT
,TO_CHAR(B.TIME,'DD-Mon-YY HH24:MI:SS') TIM
FROM
(
SELECT TABLESPACE_NAME, MIN(FILE_ID) FILE_ID
FROM DBA_DATA_FILES
GROUP BY TABLESPACE_NAME
) A
,V$BACKUP B
WHERE
B.FILE#=A.FILE_ID
ORDER BY
B.TIME
-- A.TABLESPACE_NAME
;