http://dengekionline.com/elem/000/001/031/1031187/The cloth store owner who Sega did a collaboration with on Yakuza 0, appearently knows the Yakuza developer (Yokoyama) from 15 year ago.
What I could tell about the section of the interview that was about Jet Set Radio:
Yokoyamas first year at Sega, was planner on Jet Set Radio.
Jet Set Radio was announced at a club? Could be understanding wrong...
Connection of portrayals of Japan in JSR and Yakuza.
Jet Set Radio staff was very much the "first" generation of todays Yakuza staff.
Wish someone could translate the interview...