No, it didn't in the GMOD package at least. On Steam, I think the Source multiplayer pack is equal to the retail CS:S. But I can't open the multiplayer pack on the Steam store, so they must have gotten rid of it at least during the sale.
Well $5 is still a good deal for the single game. But for $20, it's better to buy the game at a local store (Gamestop, we always carry the game) and it comes with DoD and Half Life 2 Deathmatch.