The following code puts the label on the left of the divider. When you resize the window the label is moved to the right.
 
    HBox h = new HBox();
    SplitPane ui = new SplitPane();
    ui.getItems().addAll(h, new Label("XXX"));
    Scene scene = new Scene(ui);
    stage.setScene(scene);
    stage.setVisible(true);