I understand the need for migrating roles but why do you need to create users as the JOB in PPM can do so. Also from tenant level export i.e. exporting from PPM you can export folders only and all its association will be exported. However if you just want to export roles and you are an on premise then you need to login as Superuser and export user with roles and also you need to ensure the destination org ID is same.
However this is not allowed in