Your library must be initialized before it can be used, to register the new types that it makes available. Also, the C library that you are wrapping might have its own initialization function that you should call. You can do this in an init() function that you can place in hand-coded init.h and files. This function should initialize your dependencies (such as the C function, and gtkmm) and call your generated wrap_init() function. For instance:

void init()
  Gtk::Main::init_gtkmm_internals(); //Sets up the g type system and the Glib::wrap() table.
  wrap_init(); //Tells the Glib::wrap() table about the libsomethingmm classes.
} genera la implementación del método wrap_init() en, pero la declaración en wrap_init.h se programa a mano, por lo que necesitará ajustar wrap_init.h de manera tal que la función wrap_init() aparezca en el espacio de nombres de C++ correcto.