While there is no obvious source that confirms that 昼田洋二 is romanized Yoji Hiruta, 昼田洋二 is always credited as (tenor) saxophone player. A few japanese sites provide the romanization Yoji Hiruta for a sax player (without mentioning the original kanji name), among others
this board. Fortunately they even link to
Tsuyoshi Nagabuchi's Official Web Site which says that
Yoji Hiruta (Sax) is part of his live band. The
japanese wiki entries for Nagabuchi's live gigs confirm my assumption that 昼田洋二 is actually Yoji Hiroto.