Well, not quite right, wife in Japan and all.
For example, the name Katsuhiko is a normal guy's name. The trick is, in Japanese "-ko" and "hiko" are 2 separate Kanji. So, it doesn't necessarily work to say "all names ending in ko are girls' names." It's just that all names ending in "-ko" based on the Kanji for "child" are girly names.
That said, I just flipped through the first names and found the following suspicious girly names:
Miyoko
Ryoko
Shigeko
Yuko
It may be possible for some of these like "Yuko" to be guy's names if they're really long vowels like "Yuukou".
F. Montoya, you around?