If you write a Qt application (e.g. Qt Quick with or without a C++ backend), sure. If you write a pure Gtk+ (or, rather, Hildon) application, it's possible.

However, the point here is that you can start developing apps for MeeGo now, and target Maemo 5 and Symbian and, ultimately, MeeGo by using Qt.

Similarly, since Qt is now Nokia's official story - even for Maemo - Maemo apps developed in Qt have a very good chance of running on MeeGo.

But a lot of Maemo apps integrate into Maemo in specific ways, which means the UI toolkit is one of the smallest problems; so don't get too overoptimistic.