Thanks for your interesting thought.
Oda appears to have plentiful of wildly extended imagination on using various elements, creatures, beings, species and lifeforms to create his series of characters.
Those you have stated are pretty accurate. But I'll add some notes to those not stated.
Smoker - his epithet is "Smoker the White Hunter" - though he may not be an animal himself but he is a hunter. A hunter hunts (obviously). In our context, a hunter hunts for animals. In the One Piece World, Smoker is Marine soldier and therefore he hunts pirates, and brings them for persecution. Pirates in the eyes of Marines are considered lower beings (so to speak). It's like police trying to catch criminals. Lower doesn't mean discrimination though in some way or another, it may happen. But it has the element of guilt and condemnation in that sense.
Wapol - He's a king in Black Drum Kingdom. Though he is not an animal, but he eats a lot and as and when he likes, and eats non-stop. He is definitely a glutton. He also has a habit of saying "kaba" which means hippopotamus in Japanese.
Big Mom - Though not specified, doesn't she look (and behave) like a witch? (Or at least the impression of it?)
Brulee - Big Mom's daughter - likewise, she resembles her mother, doesn't she?
Blackbeard - Going round stealing devil fruits, gives me the impression like a theft.
Kaido - He has the epithet as "King of the Beast". He has the appearance of having very long, thick, swept-back black hair that resembles a mane, curved horns on his head and a black and gold tattoo resembling reptilian scales. Though he isn't described as any kind of a creature, but his beastly look does give him away.
Shanks - He isn't an enemy to Luffy and he is not taken as a villain, at least not at the moment. But his red hair is a unique feature of his and obviously that's how he earns his epithet. He does look very human. His name is rather interesting. Shank (or plural shanks) means a person's leg, a lower part of an animal's foreleg or the shank of an animal's leg as a cut of meat. I'm unsure what Oda has in mind when he uses this name, but if we think of linking to an animal for example, the animal's foreleg probably fits the bill. Do note that forelegs are the front legs of a four-footed animal.
In one way or another, characters in One Piece may tend to have a relation to some form of animals, creatures, beings, or lifeforms. Even Brook's soul is "spiritual" or very supernatural.
