CREATE VIEW my_view AS
SELECT a.*, b.* 
  FROM table_a a
  JOIN table_b b
    ON (a.ID = b.ID_A);

SELECT v.*
  FROM my_view AS OF TIMESTAMP systimestamp - INTERVAL '30' SECOND v;  

SELECT a.*, b.* 
  FROM table_a AS OF TIMESTAMP systimestamp - INTERVAL '30' SECONDa
  JOIN table_b AS OF TIMESTAMP systimestamp - INTERVAL '30' SECONDb
    ON (a.ID = b.ID_A);

Yes, you can use point in time (as of) flashback query on views:

create table t1 (
  c1 int
);
create table t2 (
  c1 int
);

create or replace view vw as 
  select * from t1
  join   t2
  using  ( c1 );

insert into t1 values ( 1 );
insert into t2 values ( 1 );
commit;

exec dbms_session.sleep ( 10 );

insert into t1 values ( 2 );
insert into t2 values ( 2 );
commit;

exec dbms_session.sleep ( 10 );

insert into t1 values ( 3 );
insert into t2 values ( 3 );
commit;

select * from vw
  as of timestamp sysdate - interval '15' second;
  
C1   
    1
  
select * from vw
  as of timestamp sysdate - interval '5' second;
  
C1   
  1 
  2 
  
select * from vw;

C1   
    1 
    2 
    3 

Though the versions between syntax is unsupported:

select * from vw
  versions between timestamp minvalue and maxvalue;  

ORA-30051: VERSIONS clause not allowed here

To verify what's going on here, you can pass your flashback query to dbms_utility.expand_sql_text. This shows you the full statement the database executes.

Do this and you'll see that the as of clause is pushed down to each table, ensuring you get the values from each table at that time:

declare
  l_clob clob;
begin
  dbms_utility.expand_sql_text (
    input_sql_text  => q'!select * from vw
  as of timestamp sysdate - interval '25' second!',
    output_sql_text => l_clob  );
  dbms_output.put_line(l_clob);
end;
/

select "A1"."C1" "C1"
from (
  select "A2"."C1_0" "C1"
  from (
    select "A3"."C1" "C1_0"
    from "CHRIS"."T1" as of timestamp (sysdate - interval '+00 00:00:25.000000' day (2) to second (6)) "A4",
         "CHRIS"."T2" as of timestamp (sysdate - interval '+00 00:00:25.000000' day (2) to second (6)) "A3"
    where "A4"."C1" = "A3"."C1"
  ) as of timestamp (sysdate - interval '+00 00:00:25.000000' day (2) to second (6)) "A2"
) as of timestamp (sysdate - interval '+00 00:00:25.000000' day (2) to second (6)) "A1"

So yes, your two queries are equivalent.