Momo is also one of them but I never said anything about a DBZ connection. It's the fact that a super powerful being in One Piece verse. There's also one just like it in DBZ. It's the story behind it, not the visual.
Point is Oda didn't necessarily see Shenron and decided he wanted to use an Asian dragon because of that
Dragons are godly beings on Eastern folklore, so what better way than to base a powerful villain on one?
–- Update From New Post Merge ---
I’m surprised Kaidou is such a prominent Figure in Wano. There’s festival Dedicated to him, he is literally called the king of Wano(Meaning the Shogun is just a military title), he is called wise(I guess it’s just a stereotype of him being a dragon since he certainly doesn’t seem wise), and he Freakin makes public appearances in Dragon form… This is really shaping up to be like some Spirited Away Level shit, Ridiculous magical beings pop up left and right and people just take it at face value like “Uhh, It’s a dragon, it must be wise”... But then again O-Tsuru almost bit the dust the moment she insinuated that the Factories that we’re pollluting the place we’re Kaidou’s doing so it seems there’s a ridiculous gag order as well in some places.
Observations: The festival is said to be celebrated by the people from the Capital but as a facade, and Kaidou polluted the outskirts of the capital and regularly sends his henchmen to reek havoc in the place. Also on entering Bakura town, there’s mention that there’s border patrol even for towns meaning it must exist for the Capital as well.
My conclusion is that the people in the Capital have been kept completely oblivious of the Tyranny of Kaidou, first by feeding their kids propaganda in schools about Orochi the great Warrior and Kaidou the dragon king, then there’s the border policies that limit access to the outside world so people can’t even tell how much of a wasteland their country has become. There’s also a gag order around this that is publicly exercised outside the flower Capital with stuff like Otsuru almost getting killed in plain sight and it’s probably covertly exercises in the Flower Capital with assassinations and shit like Zoro getting falsely accused of a crime to get him to kill himself. This is basically a dark twisted version of Spirited Away with the Wise dragon king, the elegant Rokurobi Teacher, the gallant Shogun Orochi, all the freaky Headliners and gifters, and freaky mutant animals are evil and the Both the people who accept the Yokai(a la Spirited Away) and the people who resist them are all getting screwed.
Some questions though. What is the point of this Charade? Why not subjugate everyone including the flower Capital people? Or why not let everyone at least live a semblance of a human life? We’ve seen this sort of thing before in different capacities. Wapol thoroughly believed complete subjugation was the only way to be a true ruler so he never even made a charade. Crocodile kept up a charade for the sake of actually becoming the head of Alabasta’s military but Kaidou already has the Shogun and a stronger military than the shogun’s via the Beast pirates. Doflamingo created a charade to give himself legitimate claim to Dressrosa’s Throne by feeding off people’s willingness to hate the previous monarch but that’s the Shogun’s thing not Kaidou’s. Momma herself also doesn’t use Charades to rule Totland and she’s just legitimately misguided in her beliefs in general. As of now, there seems to be need for a reason why Kaidou even bothers with all this, and I’m guessin that will be a later in the arc revelation since no one in the main cast actually cares to know why Kaidou’s doing any of this.
He probably knows that a kingdom cannot stand if all it's people are oppressed and hate him, so the charade was necessary for its citizens to willingly and happily serve him. A cheerful nation is more powerful than an oppressed and sad one.