Yamato fighting or no, no make any difference, Greenbull would continue to grow his forest "infinitely" and at one time or another would trap and drain it. Yamato could hold out for a while and land a few coc attacks with his hybrid form, but nothing that would harm him on general levels.
Unlike others, Yamato showed already will give GB so much trouble
Plus her powers can easily freeze his plates
GB can't beat dukes + Yamato + Momo at once
He can only restrain but then they'll keep breaking free with Momo or Yamato using their powers