Yoshitate Kyounosuke is the voice provider of Nekomura Iroha. Initially, Kyounosuke comedically denied this, but confirmed it for the release of Iroha's V4 edition.
As for Kyounosuke's gender, on many social accounts he is listed as male, including on his personal blog and his Facebook account. HIs sister Fuyu lists him as her older brother. As recently as on the comments of a Dec 2013 live performance of Senbonzakura, Kyounosuke directly corrected a fellow commenter who had addressed him as a 'woman' in their comment, stating, "Sorry.I'm not woman."
Whether Kyounosuke was born male or not does not so much matter as what he says he is now.
Since it's clearly not going to be deleted by any moderator, and because the utaite wiki finds this significant as a sort of time capsule (it also turns up as the second result on Google when searching his name), I have preserved the original response below, which was given before 2013:
"Okay, first things first.
Kyounosuke Yoshitate is a proffessional nico singer known for her vibrato singing style and her old japanese language covers of vocaloid songs.
Before their first vocaloid releases, Yoshitate worked with AHS software for Soundpool, a collection of royalty free samples for use is music software. She sang Tsubasa, thus becoming the first to sing this song. AHS later used Tsubasa as a demo for Kiyoteru Hiyama.
Sometime later, Iroha Nekomura was released. Her two demos were Abbey fly and Tsubasa. At some point after that, a thread opened in 2ch, showing both the version sung by Yoshitate and the version sung by Iroha. Comparisons followed and people started speculating Yoshitate being Iroha's voice provider.
However, Yoshitate herself denied it, calling Iroha a "wierd hello kitty robot girl". Even after that though, people still speculate her being Iroha's voice provider.
About her being born a guy, it was something that spawned from the VocaloidOtaku forums. A user posted a link to her facebook page and noted that she was adressed as male on her page. This made a few people wonder if she is male, when another user posted a picture from her blog in an effeminate style, leading to the belief that she is transgender."