No. It will only show discharging.
Battery charging will not show because the path of least resistance between the alt and the battery will be the new wire.
That's not just theory @Mopar Tim and others can tell you.
Stick one of those voltmeter's in the lighter socket. That will then give you some idea of whether the system is working. Might have to pull it out when the key is off. Sometimes they are wired to a fuse that's always hot.
