Nah, not gonna happen. Well, I would be overjoyed if Meloetta decided to join him but that would be the only case. He wouldn't catch them, they would join him, that's the only possibility Satoshi could ever obtain a legendary Pokémon. But as others mentioned, if it were to happen, it would be a cute little legendary, not some powerful one.
@PikaPii: I'm curious how you thought of Cobalion or Deoxys =D