It's like an unwritten rule of youtube: if there's a song, you can probably find nightcore of it. Unless it's, like, classical music, or some other genre that doesn't appeal to the average viewers of nightcore videos. There's also Scatman nightcore. I don't question it. It's a somewhat futile resistance.
It is now. They used to be their artist, but something happened ( I don't remember what) but now basically, yeah, it's sped up music. You can probably still find some originals here on RU-vid somewhere.