I read that it was a girl's name on a name site. This is the first time I have seen it as a boy's name. Though I did look at you wiki links! I saw that Shinobu Asagoe, Shinobu Otake and Shinobu Nakayama are mentioned on Wikipedia as well and they are all girls...so I think it is like you said, it is unisex. Because both male and REAL life female girls (not just in Mangas and Animes) are being named Shinobu in Japan. Kind of like Yuki and Momiji (though I don't think Momiji is common and Yuki I found to be commonly used with other letters to denote a girl or boy like Yukio and Yukiko).