Maybe OP is onto something. I'm not saying it's Kai D. Ou, but it makes sense for Kaidou of the Beasts to equal Sea Ruler of the Beasts. Oda could have intentionally combined Kai and Ou into Kaidou for this allusion.True, also his epithet already "Kaido of the beast"
It also fits in with the fact that Kaidou is a Yonko, which means Four Emperors, and an emperor is a ruler.