tribe_get_wooticket_amount()

// Returns the amount of active WooCommerce tickets for this event
// Mostly useful for detecting if an event has tickets. Returns 0 for those.
function tribe_get_wooticket_amount( $event_id = null ) {

    if ( is_object( $event_id ) )
        $event_id = $event_id->ID;
    if ( $event_id === null )
        $event_id = get_the_ID();

    $query = new WP_Query( array( 'post_type'      => 'product',
        'meta_key'       => '_tribe_wooticket_for_event',
        'meta_value'     => $event_id,
        'meta_compare'   => '=',
        'posts_per_page' => - 1,
        'fields'         => 'ids',
        'post_status'    => 'publish', ) );

    return count($query->posts);
}