I believe that this is just a bug....using Network and Service group definitions is allowed all over the UTM Webadmin GUI except in this particular section.
At every webadmin box, where you can add objects, you can click on the green plus and then select type of definition to see, which types are supported. In this case there are no services groups allowed.
At every webadmin box, where you can add objects, you can click on the green plus and then select type of definition to see, which types are supported. In this case there are no services groups allowed.