populate a field, el 'emaito' es el parametro de populate q se setea.

populate

add_filter('gform_field_value_emailto', 'add_job_email');
function add_job_email($value)
{
    global $post;
    $id = $post->id;
    $email = get_field('email_to', $id);

    return $email;
}