It's not directly mentioned in the scans, but Kenichi Maeyamada said in the description of
https://www.youtube.com/watch?v=osWXbe7MbGE that he sang the vocals of Hyadaruko. In the booklet, Hyadain's lyrics are colored blue, Hyadaruko's are pink, and Sasaki Sayaka's are orange. Furthermore, the karaoke title of track 4 explicitly excludes Hyadaruko. So Hyadaruko should be added to the performers list.