Well, after u watch this video.
http://youtu.be/8yChUupd3bo
I at first thought it was some sort of exploit. I would have preferred that, because it apparently was a full on glitch/server error that kept them invisible. A bit after i put up this video i was killed by "invisbile" siege, which my group said were not invisible. Or maybe it is some exploit, but I honestly think this is just SUPER BUGGY Zenimax's Elder Scrolls Online Beta part Duex.