What technique should be used in multi-view app (using CompositeViewer) if some nodes look differently in different views? For example, if some label positions should be recalculated depending on the view's camera parameters? Or if some other kind of annotations (rectangular area with a border some text) are visible or hidden depending on the view scale?
osg has Billboard and Text classes that handle orientation for each camera out of the box (see for instance how the CullVisitor applies to the Billboard class here).
To implement other behaviors which depend on the camera, the right place to make things happen is a Cull Callback added to your nodes: your callback will be invoked multiple times (one for each different camera) on every frame, and you can react accordingly to your needs.