A workaround for requiring that users fill out the RH Date field. Fails checkout if date is still the same as today's date.

pmprorh_required_date.php

<?php

// Copy from below here...

/**
 * Add a "Birthday" field via Register Helper.
 */
function my_pmprorh_init() {
	//don't break if Register Helper is not loaded
	if(!function_exists( 'pmprorh_add_registration_field' )) {
		return false;
	}
	$checkout_area = 'checkout_boxes';
	$fields = array();
	$fields[] = new PMProRH_Field(
        "birthday",
        "date",
        	array(
			"label" => "Birthday", 
			"profile" => true,
		)
	);		
	//add the fields into a new checkout_boxes are of the checkout page
	foreach($fields as $field)
		pmprorh_add_registration_field(
			$checkout_area,				// location on checkout page
			$field						// PMProRH_Field object
		);
	//that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action( 'init', 'my_pmprorh_init' );

/*
 * Throw an error if RH date field is still today's date.
 */
function my_pmpro_registration_checks_birthday( $okay )
{
	global $pmpro_msg, $pmpro_msgt, $current_user;
	$birthday = $_REQUEST['birthday'];
	$today = strtotime(date('Y-m-d'), current_time('timestamp'));
	$year = date("Y", $today);
	$month = date("n", $today);
	$day = date("j", $today);

	if ( $birthday['y'] === $year && $birthday['m'] === $month && $birthday['d'] === $day ) {
		$pmpro_msg = "Please fill out the Birthday field.";
		$pmpro_msgt = "pmpro_error";
		return false;
	}

	return $okay;
}
add_filter("pmpro_registration_checks", "my_pmpro_registration_checks_birthday");

Additional checks for if day or year fields was left empty to prevent defaulting to epoch Jan 1, 1970 when day field was empty.
https://gist.github.com/ipokkel/829397eec71c717ef2765affb5244f41