Using with clause

Question

I am using the sql with following construct , the explain plan doesn't show that index on col1 of tab1 (used in with clause) as used- it just shows a full table access of a view (system) - result set of query in with clause.
1. Is it that oracle will not use that index or it doesn't show up
2. If so then is it good to have that table in join of all the three sqls that i am doing union - atleast in that case the index on col1 gets used (per explain plan).
with sql1 ( select * from tab1 where col1 = 'y')
select col_gen
from tab2 a, sql1 b
where a.col3 = b.col3
union
select col_gen
from tab3 a, sql1 b
where a.col3 = b.col4
Union
select col_gen
from tab4 a, sql1 b
where a.col3 = b.col4

Answer 1

WITH tab1 AS ( SELECT * FROM tab12 WHERE SESSION_ID = '12')
SELECT DISTINCT b.unit_key unit_key ,NULL colabc1_KEY ,NULL colabc3_KEY,a.col3_ID
FROM tab1_col31_MAP a, tab1 b
WHERE a.unit_id = b.unit_id
UNION
SELECT DISTINCT NULL unit_key ,b.colabc1_KEY colabc1_KEY,NULL colabc3_KEY,a.col3_ID
FROM tab2_col32_MAP a,tab1 b
WHERE a.colabc1_id = b.colabc1_id
UNION
SELECT DISTINCT NULL unit_key,NULL colabc2_KEY,b.colabc3_KEY colabc3_KEY,a.col3_ID
FROM tab1_col33 a, tab1 b
WHERE a.colabc3_id = b.colabc3_id
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=CHOOSE                                        
RECURSIVE EXECUTION     SYS_LE_2_0                                   
TEMP TABLE TRANSFORMATION                                        
SORT UNIQUE                                        
UNION-ALL                                        
NESTED LOOPS                                        
VIEW                                        
TABLE ACCESS FULL     SYS_TEMP_0FD9D6603_53EE226                                   
INDEX RANGE SCAN     SYS_C00133240                                   
NESTED LOOPS                                        
VIEW                                        
TABLE ACCESS FULL     SYS_TEMP_0FD9D6603_53EE226                                   
INDEX RANGE SCAN     SYS_C00133205                                   
NESTED LOOPS                                        
VIEW                                        
TABLE ACCESS FULL     SYS_TEMP_0FD9D6603_53EE226                                   
INDEX RANGE SCAN     SYS_C00133202                                   
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
SELECT * FROM tab12 WHERE SESSION_ID = '12'
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=CHOOSE                                        
TABLE ACCESS BY INDEX ROWID     tab12                                   
INDEX RANGE SCAN     IDX     
Will the temp table transformation use the index used in the query above (ie. IDX)