If G5 can fodderize Zoro then either Luffy should have used G2/G3 to beat awakening Lucci or awakening should be beating 2 swords Zoro. But that didn't happen so Luffy can't.
No, Jinbe is there to witness Zoro's strength. Just like what happened with Monet and Tashigi.
Tashigi purpose was to witness Zoro's strength.