You can look at the $scope.executives
array in your controller to find out which users are selected. If a user is selected, they will have a addto
property.
So your code might look something like this:
$scope.submit = function(){
var selected = [];
angular.forEach($scope.executives, function(executive){
if(executive.addto){
selected.push(executive.user.id);
}
});
//Do something with selected...
}