Function like is_registration_page to check if current page is registration page

You can use is_admin to check to see if the current web page is part of WordPress’ administrator interface.

Is there a way to see if the page being processed is the registration page?

You could create your own simple function.

function is_registration_page() {
    if ( $GLOBALS['pagenow'] == 'wp-login.php' && isset($_REQUEST['action']) && $_REQUEST['action'] == 'register' ) {
        return true;
    }
    return false;
}