I love these messages, I study them as a hobby, but I actually think this is a coincidence. Here's why:
1) James' voice is still in character.
2) I wouldn't have known what he said unless I was actually told. I only made out the message when they told me at the end of the video.
3) The line when played in reverse, although clear, doesn't sound fluent. It sounds broken.
Although I have heard cases of hiding messages in cartoons, so it's a possibility. This is actually the first time I've said one of these messages was a coincidence (backmasking supporter see) as it's Pokemon. Okay, the creator's are cheeky enough to create a pokemon with a cry sounding like a fart (Skuntank) but not to insert devilish messages. If one listens to something enough, they can make anything out of it.
In other news, here's the "I Love Satan" clip everyone's raving about. Just click on the Pokemon Rap one on the right.
Clicky