>>55824200Remember. In the debut episode of this specific Snubbull, she almost got married to another Snubbull. So because of that episode, we know that it is canon that Pokémon can marry other Pokémon.
Sinnoh Folk Story 3 says humans used to marry Pokémon but don't anymore. That means you can't marry a Pokémon if you are a human but you can marry a Pokémon if you are also a Pokémon.