Is the IDE plug-in (org.eclipse.ui.ide) considered part of the Rich Client Platform?
No. The org.eclipse.ui.ide plug-in is layered on top of the generic workbench (org.eclipse.ui) and adds IDE-specific views, preference pages and other extensions. The IDE uses the workspace resource model as its underlying data model. :The org.eclipse.ui.ide plug-in, and the extensions defined within it, are not part of the Rich Client Platform, but they can be used in a resource- (and workspace-)based RCP application.