I attempted to create a user object from a base sheet and then change the owner of that object to anther user who was a root admin, though I could see it as an admin in the QMC I could not see the actual sheet in the hub. Let me communicate this in the org and see if we can find out more.
Changing the sheet ownership is not enough, the app owner would need to change as well for the sheet to appear in the app.
I see where this is going. You want to make it possible for one user to see another's work before it is published. While technically it may be possible to have an app show up in the my work area of two users and have the sheets appear as well, it is an unsupported configuration and may cause app corruption in the app and/or sheets if two users try to view or save the same sheet to an app at the same time.
You may want to have a look at Architeqt on Branch. With this solution, it is possible to create application blueprints. The admin could potentially use the blue prints to monitor and review the developer's work.