Yes, the battery warranty would cover the BMS. It might be tricky to get a dealer to order three expensive parts without them doing their own diagnosis. Zero screens orders of those parts, so they would call and ask why the dealer was ordering those. For Zero to cover anything under warranty, it'd have to be looked at by a Zero tech and probably a Zero HQ engineer. They also have to be programmed to each individuals bike, and Zero is not open on weekends. Zero HQ is evacuated due to wildfires, but I think order for Zero HQ was lifted, so hopefully they'll be back to ship parts sometime next week.
I guess it's a bit of a gamble, but Zero would probably discount/warranty more than you'd save by ordering out of pocket. Looking at about 400 for an MBB, 550 for the BMS, and 370 for the DCDC, plus probably 2-3 hours shop labor replacing all those things.