It lists in the features that Contango features a drop down menu,
Yes, DesignOrbital themes support WordPress Menu that was introduced in WordPress 3.0
I can’t for the life of me figure out how to put a category in the menu and have the articles show up in a drop down list.
Practically, you can add any item (i.e. category link, pages link, post link, custom link etc) to the menu with few clicks and much power. Following articles will be helpful to you,