Hi Georg,
From our CA Support perspective, if a customer is on an unsupported release and faces a problem that is caused by this they will be advised to upgrade to a supported platform as first step. Being on unsupported release does not 'guarantee' issues but provided we never tested and certified the platform, we most definitely expect more issues we didn't account for.
Now regarding your question - I don't know if there will be a specific problem with 12.1.0.1, however in some cases CA PPM detects the database level is not correct and in that case it may not even allow you to log in. It will give you an error message in app-ca.log about invalid tenant or database configuration. So I would advise you to make sure it will even work before proceeding with the planning.
Hope this helps -NIka