Yes. Log in with your SwissPass profile under Profile -> Login. Based on the login and the information stored there, the BLS Mobile app recognizes that you are in possession of a Half-Fare Card.
Under the tab Sub, it shows you your Half-fare Card. This allows you to purchase your tickets at a reduced price.
If your Half-fare travelcard is not linked to your SwissPass login, you can select your Half-fare travelcard under Profile -> App-Settings.