All tabbed dialogs that use CAdUiTabMainDialog and CAdUiTabChildDialog can be easily made tab extensible. There is no limit for the number of tabs that can be added to a tab-extensible dialog. If the main dialog is resizable, added tabs can participate in that resizing using the same directives outlined in the documentation on resizable dialogs. All dialogs in AutoCAD use scrolling tabs as opposed to stacked tabs.
It is important for you to set the dirty bit for the extended tab using the SetDirty() member function of CAdUiTabChildDialog when data needs to be initialized or updated via DoDataExchange.