I suppose you could try referencing <tab idMso="TabAddIns" visible="true" >
and see if that works, but why would you even want to display that tab? It
makes finding your UI quite difficult, especially if there's more than 1
addin that uses CommandBars for Inspectors.
In the early days of testing Outlook 2007 at one point I had 4 addins
running that didn't use the ribbon and it was almost impossible to find
their UI in the AddIns tab and things were just butt ugly with buttons for
different menus, toolbars and additions to the Standard toolbar all bunched
together in a group for each addin. Yuck!