Hi Purpleedge,
currently the only way to add categories to the main menu is through wordpress menu interface adding them 1 by one.
In that case the category link will be displayed no matter if the category is empty or not.
Given that this would be a wordpress hack, rather than a GD hack, I’ve googled “wordpress menu hide item if empty category” and I haven’t found a proper hack that would hook into the wordpress menu to hide empty categories. In wordpress forums the answer is:
If you’ve added a link for a category to a custom menu, you can’t then dynamically hide it “on empty”. Just don’t add these links to your custom menus(s) unless you have at least 1 post in the relevant category.
and even though it is 3 years old, I haven’t found anything that wouldn’t require hacking the theme menu, like explained here : http://wordpress.org/support/topic/hide-empty-categories-in-wp_nav_menu
So, it doesn’t seems like there is any easy hack for this…
Thanks