Query to find users with passwords same as their username in Oracle
I don't think this is possible for current versions of Oracle. What I understand happens is that Oracle generates an instance-specific salt and adds this to the passwords being hashed using the SHA1 algorithm, the result of which is stored as the hashed password. See for example http://marcel.vandewaters.nl/oracle/security/password-hashes for information about this algorithm.

This means that password hashes are installation specific, and I don't think it's possible to generate the expected hash value for a given username/password combination.

What you need to do is as @elfcheg suggests to add a password_verify_function on all profiles, or to a single profile, and assign this profile to all users.