These are the same person. He's a programmer that worked on some C64 games, and also several Digital Pictures joints, including a cameo in some FMV. The Joe Vierra page should remain - he's only credited as "Joey D. Vierra" in one game (Prize Fighter).
I've moved that lone credit from the Joey D page to the Joe page, so the Joey D page is now empty. "Joey D. Vierra" would then be added to the Joe page as an Alias. Phew.