The documentation says that the User who performs the Migration (user name provided as part of the Connection details to the Source Database) has to be an Database Administrator. This is because the user requires access to e.G. Oracles system catalogs to be able to perform a Migration.
The issue is that the 'Apply Connection' action should not only check if the given connection could be established but it should also check if the Connection was established by using a user with DBA privileges.