When the FXML file contains an fx:include, the hierarchy panel should display some dedicated icons/text.

Load the attached included1.fxml which includes included2.fxml.

With SB 1.1, when loading include1.fxml, you will get 1 more icon to indicate this is an include + the root class of the included2.fxml (in this case, an AnchorPane).
With SB 2.0, when loading include1.fxml, you will get a default question mark icon + fx:include text.

See screen captures.