Not sure if you still need this but you would have to use the API in one way or another. Check the following events:
http://www.smartmenus.org/docs/#beforeshow
http://www.smartmenus.org/docs/#show
You could check if any sub menu is visible at any given moment, for example, like this:
var $subMenu = $('#mySubMenu'); // the id of the UL element
if ($subMenu.is(':visible')) {
// ...
}