Very good comparison with the Dynasty Warriors, Thedevil. I keep playing out the scenario in my head of the crew all taking on a mob of several hundred zombies and i just can't get over its amount of ass-kickery
I somehow see Chopper as not being able to do much compared to the rest, though he could move quickly, possibly treat an infection, and his Guard Point could help keep him from being bitten too easily
Nami's biggest role, i think, would be acting as the brains. Without her around, I can imagine Zoro, Luffy and Sanji just barging into the horde of zombies until it's too late to fall back.
I'm also not sure, but since Luffy's made of rubber, i don't think that a zombie bite could pierce his skin. I mean, Arlong could, but teeth were beartraps. Zombies seem to just grab and tear with their teeth, so i except they'd just keep stretching him out. I still think he could get overwhelmed (especially while waiting for his Gomu Gomu attacks to recoil back to him). I can also totally see Luffy getting mad and biting a zombie back. Then you've got trouble…
Also, i have my doubts that Robin could be infected by biting her extra limbs. She seems to be able to feel things with them, but when she was keeping guards from the gates in Alabastia, someone cut her and while she felt the sting but didn't bleed. Still, a bite would probably be enough to chase away that limb, even though she'd probably snap their heads off before that