IT was Stated that you need both eyes to UNLOCK susano but maybe once IT has been unlocked you are free to activate IT whenever you want to. Its like a box you need keys to open IT but once IT has been opened you can throw away the keys but still open the box.
Madaras real original eyes are indeed "active", obito has one, zestu got the other. So technically his eyes were indeed in the real world "active", he just couldn't use his right eye ability or left eye ability (I.e. Tsukuyomi, amateratsu)