I suspect that they aren't found in exactly the same place. I was told by a supplier some years ago that they don't find bimaculatus when looking for bimaculoides becuase they aren't found at the same depth and they like different habitats. And in fact, they always provided O. bimaculoides.
According to Mark Norman's book, Cephalopods of the World, O. bimaculatus is found "on rocky reefs to depths of 50m". Bimaculoides "typically occurs on mud and sand habitats, as well as on rocky reefs to depths of at least 20m
Of course, they're closely related and probably overlap in some areas. I wish we could get a more exact idea about where along the California coast each species is found.