Oh, they are. And no, you shouldn't take your chances. But if you're Sora's toy until you get home, you couldn't have a better owner to keep you safe. People like him and me that have Keyblades are the best at taking down Heartless. There isn't a better Keyblade wielder than him.

And he still acts like a kid if you haven't noticed.

Heartless are the darkness and heart of a person. Nobodies are everything that's left: the body and soul. Nobodies are rarer since only people with strong hearts can make them.