Correct, provided you have also a computer running iTunes between your network disk and appleTV. Which kind of makes NAS obsolete. You can as well have a simple USB drive (a DAS) connected to your computer and stream to aTV.
Due to Home Sharing authentication mechanism (that apparently goes via iTunes Store account), there is no way to let aTV access the NAS directly, as no NAS on the planet currently knows how to serve content to aTV and also handle the authentication.
Synology has some sort of workaround, but you still need a iOS device to kick off the playback.