I don't think that Tab Manager will do what you want. IIRC, Tab Manager will only move the icon from one tab to another. I'm not aware of any tool that will duplicate an app's icon onto another tab.
I haven't tried it (Qtopia may have issues with the same app on different tabs, or the same app registered for a given MIME type more than once), but, in theory, you should be able to achieve what you want to do, if you have any Linux command line experience:
The icons on each tab correspond to a file with a .desktop extension. They are located in a hierarchy of directories in /home/QtPalmtop/apps. The contents of each subdirectory reflects the contents of the tab with the same name (Applications, Settings, etc.). So, if you wanted the icon of the addressbook app, for example, to appear on both the Applications and Settings tab, you simply need to copy Applications/addressbook.desktop to Settings/addressbook.desktop. You then need to restart Qtopia or refresh the launcher in order to see the change.