Чтоб эмулировать асинхронность используем setTimeout

app.controller('DemoCtrl', function ($scope, $http, $timeout, $interval) {
  var vm = this;
  vm.personAsync = {selected : "wladimir@email.com"};
  vm.peopleAsync = [];
 
  $timeout(function(){
   vm.peopleAsync = [
        { name: 'Adam',      email: 'adam@email.com',      age: 12, country: 'United States' },
        { name: 'Amalie',    email: 'amalie@email.com',    age: 12, country: 'Argentina' },
        { name: 'Estefanía', email: 'estefania@email.com', age: 21, country: 'Argentina' },
        { name: 'Adrian',    email: 'adrian@email.com',    age: 21, country: 'Ecuador' },
        { name: 'Wladimir',  email: 'wladimir@email.com',  age: 30, country: 'Ecuador' },
        { name: 'Samantha',  email: 'samantha@email.com',  age: 30, country: 'United States' },
        { name: 'Nicole',    email: 'nicole@email.com',    age: 43, country: 'Colombia' },
        { name: 'Natasha',   email: 'natasha@email.com',   age: 54, country: 'Ecuador' },
        { name: 'Michael',   email: 'michael@email.com',   age: 15, country: 'Colombia' },
        { name: 'Nicolás',   email: 'nicole@email.com',    age: 43, country: 'Colombia' }
      ];
  },3000);
 
}

Шаблон вывода

  <p>Selected: <pre>{{ctrl.personAsync.selected | json }}</pre></p>  
  <p>List Count: <pre>{{ (ctrl.peopleAsync || []).length }}</pre></p>
  <ui-select ng-model="ctrl.personAsync.selected" theme="select2" ng-disabled="ctrl.disabled" style="min-width: 300px;" title="Single property binding with async data">
    <ui-select-match placeholder="Select a person in the list or search his name/age...">{{$select.selected.name || $select.selected}}</ui-select-match>
    <ui-select-choices repeat="person.email as person in ctrl.peopleAsync | propsFilter: {name: $select.search, age: $select.search}">
      <div ng-bind-html="person.name | highlight: $select.search"></div>
      <small>
        email: {{person.email}}
        age: <span ng-bind-html="''+person.age | highlight: $select.search"></span>
      </small>
    </ui-select-choices>
  </ui-select>
  <p><small><em>Data will be populated in 3 secs</em></small></p>