If you are trying to get a preview of the application, rendering an SBHostWrapperView won't work. You see, SBHostWrapperViews don't copy the application's render output, it simply provides a different location on the screen for the app to render to.
Instead, you can use - (SBFullscreenZoomView*)systemGestureSnapshotWithIOSurfaceSnapshotOfApp:(SBApplication*)arg1 includeStatusBar:(BOOL)arg2;
in the SBUIController
class.
That method returns an SBFullscreenZoomView, a subclass of UIView, with a snapshot of the app provided in arg1. You can use the second snippet of code you provided to get a UIImage of the SBFullscreenZoomView. That should do what you are asking, providing you with a screenshot of only a specific application.