My headcanon is that the Earth in the Pokemon universe is much larger than our Earth, all our continents with our world's animals exist on one side of the Pokemon Earth, and on the other side are the Pokemon regions, the planet being so large is the reason why they are still discovering new ones.
Anyway, considering some Pokemon species are named and after existing animals it implies those species had to exist somewhere else for Pokemon researchers to make those comparisons. Additionally one time in the anime I belive Misty talks about going to Hawaii, and in the Kanto remake there's a building selling NINTENDO SWITCHES implying that Nintendo and possibly the rest of Japan exists in the Pokemon universe.
But for an answer to the actual question... Maybe? I mean with the implications that there are real world animals in Pokemon, it is possible considering they are on far different parts of the world, but if they were on the same region/continent? Pokemon would definitely out preform and likely drive normal animals to extinction. But that doesn't mean they can't both exist separately.
