DateHydrator.php

<?php

namespace Application\Hydrator;

use DoctrineModule\Stdlib\Hydrator\DoctrineObject;

class DateHydrator extends DoctrineObject {

    protected function handleTypeConversions($value, $typeOfField) {
        if ($typeOfField == 'date') {
            if ($value == "") {
                return null;
            } else {
                return \DateTime::createFromFormat('d/m/Y', $value);
            }
        }
        return parent::handleTypeConversions($value, $typeOfField);
    }
}

MyForm.php

<?php
namespace Application\Form;

use Zend\Form\Form;
use Application\Hydrator\DateHydrator as Hydrator;

class MyForm extends Form {
    public function __construct($name, $options = array()) {
         $this
                ->setHydrator(new Hydrator($options['om']->get('Doctrine\ORM\EntityManager')))
                ->add(array(
                    'name' => 'data',
                    'type' => 'datetime',
                    'options' => array(
                        'label' => 'Data',
                        'format' => 'd/m/Y'
                    ),
                    'attributes' => array(
                        'required' => true,
                        'class' => 'form-control input-sm date'
                    )
                ));
    }

}