Yes, it is.
- You would need to teach a Skarmory the Counter from the Celadon Department Store in FireRed / LeafGreen
- Migrate it to a 4th Generation game (Diamond / Pearl / Platinum / HeartGold / SoulSilver) through the DS / DS Lite GBA function, and catch it in the Pal Park on Route 221 in the Sinnoh games or Fuschia City in the Johto Games.
- Use the PokeTransfer function in a 5th Generation game (Black / White / Black 2 / White 2) to transfer the Skarmory from the 4th Generation games in the Poke Transfer Lab on Route 15.
- Download Pokemon Bank (If you don't have it already, just be warned it costs ~5 USD per year).
- Transfer Skarmory from your 5th Generation game to the Pokemon Bank.
- Transfer Skarmory from the Pokemon Bank to the 6th Generation game.
It takes awhile, and nicely IV'd Pokemon are hard to come by in the 3rd Generation. But it is indeed possible.