No, you are unable to capture Slurpuff. However, you can capture it's evolved form, Swirlix, on Route 6 in X. To evolve it into Slurpuff, you must trade Swirlix while it's holding a Whipped Dream. You can find one by talking to a man in Cyllage City or finding one near the Baa de Mer Ranch on Route 12. Don't cry, Pokémon Y players, you can find Swirlix, too, just much later in the game. Swirlix can be found in the Friend Safari in Kiloude City if you have a friend on your 3DS that, in the game, is used to access a Fairy safari. So, Slurpuff can be obtained legitimately sooner in Pokémon X than Pokémon Y. However, you can't catch it. I'm actually training up a Slurpuff myself, so I know!