Yes… though it might not have the properties they want. It depends on how they set up things. Usually secret-service/kwallet is only useful for protecting data at rest, after the user logs out/shuts off the machine and usually software stores keys in the ‘default’ or ‘login’ keyring so it is automatically opened on login. It in no way isolates applications from each other. Implementing some keyring service in the snap would not have this unlock upon login integration.
snapd could grow a secret-service/kwallet proxy so snaps only have access to their own credentials, but in the meantime I maintain that the snap should on first launch determine if the interface is connected and provide useful information to the user on why the interface is not connected and how to perform the connection. Auto-connection in some ways hinders the user’s choice since the user must seek out the auto-connected interfaces. Storage Explorer’s security-conscious users likely don’t want password-manager-service connected (or wouldn’t if they knew that other applications had access to the objects).