You may show something in the 3D context, using OpenGL ES in the sample. A UIView could not be used for 3D rendering.
The camera image (preview you mentioned) is not a camera preview view, it is an OpenGL view drawing camera image using OpenGL.
You can always draw anything you like in OpenGL, reference the sample.
Or, if what you need is only display some UIView, find the code of status == easyar_TargetStatus_Tracked . That is the place you are looking for -- the image is recognized and tracked.