Also, about Bepo getting food poisoning, Law didn't really stay and treat him; he mostly just was like "Why would you do that?!" about eating the poisonous food. After that, even though Bepo was like "Don't leave me, Captain!", Law did leave anyway to go distract/confront Hawkins. The next time we saw Law's crewmates, they mentioned Bepo still had diarrhea, so it seems like his illness was just taking its course without being treated, like Kin'emon's. There's also the fact that whoever the traitor to Zou is knew that Raizo was on the island to tell that to Jack; we have no idea if the Heart Pirates knew that or not (or if they did, why and how they would have contacted Jack in particular). Ultimately, I don't think any of them are the traitor, and I think that scene of Bepo, Shachi, and Penguin in the prison, with them saying that the others probably won't believe them about that but they know Law will, was supposed to serve the purpose of basically confirming for us, the audience, that no, Shinobu is wrong and Law is right and the Heart Pirates aren't responsible for the stuff that's been going wrong in this plan.
Still not sure if we have enough information yet to get a solid idea of who the traitor is; everyone that we know of so far seemingly has some kind of reason for why it's probably not them: the Heart Pirates (already been discussed a bit), the Minks living on Zou (they knew where on Zou Raizo was hiding, but Jack didn't), other samurai in the alliance who stayed in Wano (they didn't know Raizo was even on Zou at all). Unless/until we get some kind of evidence that our reasoning is wrong, there are some logistical problems involved with suspecting any of them.
–- Update From New Post Merge ---
@Roronoa:
Oh, didn't remember that context precisely. May I ask which chapter this was stated?
Chapter 810 was where the Heart Pirates declared that they would fight for Zou. Nekomamushi offered Bepo and the rest the chance to sit out of the fight, since they were under his care, but Bepo refused to sit out, because it's his homeland. The others then state that it's their crewmate's homeland, with the implication that they, too, will fight for this reason.
Chapter 811 has the montage of the Curlyhats treating the poisoned and injured Minks. One panel there shows Nami helping an injured Bepo.