(Thanks Unknown_!)
*dies from hearing Ash sing*
That has to be a song created for a CD! I'm not saying it really is, because I could be wrong, but it's just too different from the ones they've had so far. Here's a list of reasons why I kinda think that...
It is almost exactly like the original version, just with some different Pok?mon related words added. Usually most people are creative enough to write their own lyrics. (If you've seen on some soundtracks, they make recreations of old classic songs.)
It's unusual hearing the characters singing instead of someone else. (They've always had some guy singing for the Pok?mon themes...) Like on Misty's Song, where that was supposed to be proof that she likes Ash. This could easily be some marketing trick for the 'proof' that Ash and May like each other. (They keep saying "Baby" and the song is It Takes Two.)
I could've sworn I heard 'One can play Pok?mon Sapphire' (And Ruby). If it's the official theme for the show, then I doubt they'd have any Pok?mon games mentioned on it that we have in real life. >_>;
Why would it be just Ash and May? There's still Masato, Brock, and maybe even Misty in the group. (Pikachu too! He could've been talking about his partner, Pikachu, but I never heard a 'Pikaaa' in the background.)
Those are my opinions, but I think they're pretty good. Nobody flame me if it ends up to be the official song though, lol! ^_^;
