If I set up Signage Sticks with the physical remote and Signage Manager Portal, can I view them in the Signage Mobile App (and vice versa)?

Yes, you can view Sticks set up with the physical remote and Signage Manager Portal in the mobile app. The reverse is also true: if you set up Signage Sticks using the app, you can also view and manage them from the web Signage Manager Portal.