$stats['totalSubmitters'] = \IPS\Db::i()->select( 'COUNT(DISTINCT video_author_id)', 'videos_videos', array( 'video_status=1' ) )->first();
заменить на
$stats['totalSubmitters'] = \IPS\Db::i()->select( 'COUNT(DISTINCT cid)', 'videos_videos' )->first();
Или на (количество всех категорий)
$stats['totalSubmitters'] = \IPS\Db::i()->select( 'COUNT(*)', 'videos_cat' )->first();