Use Elementor Pro & Elementor Hello Theme Customization on Attendee Registration Page with Modern Tribe Event Tickets.

functions.php

<?php 

/**
 * Load Elementor template if available.
 * 
 * @param $template
 *
 * @return string
 */
function redirect_virtual_templates_to_index( $template ) {
	global $wp_query;

	// If returning the index.php page run it through elementors location manager,
	// to try and load a template.
	if ( 'index.php' === substr( $template, - 9 ) ) {

		// Make sure Elementor is loaded.
		if ( class_exists( '\ElementorPro\Modules\ThemeBuilder\Classes\Locations_Manager' ) ) {
			$instance              = new \ElementorPro\Modules\ThemeBuilder\Classes\Locations_Manager();

			// Un-do page spoof settings.
			$wp_query->is_page     = true;
			$wp_query->is_singular = true;
			$wp_query->is_archive  = false;

			// Return the location of the Elementor template that is in use (if there is one.)
			$template              = $instance->template_include( basename( $template ) );

			// Get the Current instance of the Attendee Registration Template.
			$instance              = tribe( 'tickets.attendee_registration.template' );

			// Override the current pages content with the attendee registration content. (Perhaps this could be appended?)
			$instance->set_page_content( $wp_query );
		}
	}

	return $template;
}

add_filter( 'tribe_tickets_attendee_registration_page_template', 'redirect_virtual_templates_to_index', 20 );

/**
 * Use Elementor Page Settings.
 *
 * @param $posts
 *
 * @return array|null
 */
function use_attendee_registration_page_without_file( $posts ) {
	global $wp, $wp_query;

	// Only first one time for the attendee-registration page and only once.
	if ( ! $wp_query->is_main_query() || '1' !== $wp_query->get( 'attendee-registration' ) || '1' === $wp_query->get( 'elementor-attendee-registration' ) ) {
		return $posts;
	}

	// Mark that we've been here before.
	$wp->add_query_var( 'elementor-attendee-registration' );
	$wp_query->set( 'elementor-attendee-registration', '1' );

	$post = get_page_by_path($wp->request);

	if ( ! empty( $post->ID ) && 0 !== $post->ID ) {

		// Empty posts
		$posts = null;

		// Unspoof Attendee Registration Page. (Slightly.)
		$posts[] = $post = get_page_by_path($wp->request);

		// This is a single page treat it as such.
		$wp_query->is_page      = true;
		$wp_query->is_singular  = true;
		$wp_query->is_archive   = false;
		$wp_query->current_post = $post->ID;
	}

	return $posts;

}
add_filter( 'the_posts', 'use_attendee_registration_page_without_file' , 99 );