I have been building my all validation in Entity class like this...
class User { protected $inputFilter; public function getInputFilter() {
Have you tried adding the full namespace to the Validator?
array( 'name' =>'\Auth\Validator\Doctrine\NoEntityExists', 'options' => array( 'messages' => array( \Zend\Validator\NotEmpty::IS_EMPTY => 'User name can not be empty.' ), ),
),