No, it is possible for two statements to have the same hash value. The address is unique, but if a statement is replaced by another, the same address may be reused for a different statement. That's why it is common to use the combination of address and hash value to identify shared cursors. Internally, Oracle uses the full text of the statement.

select count(distinct address), count(distinct hash_value), count(*) from v$sqlarea;

Appears to show that both address and hash_value are unique columns. Does anyone know off hand if this is always the case?