You could only get zoroark if you transfer all three so no :I
I'm quite sure it only required one of the three.
When you transfer Raikou, Entei or Suicune from your games to Black & White, you will be able to get access to the Lostlorn Forest area. This area will feature a character who mentions a Pokémon that has been known to create illusions. You will find a Pokémon matching one of the beasts that you didn't transfer over. If you send over Raikou, you will see Entei. Send over Entei and you'll see Suicune and send over Suicune and you'll see Raikou. When you attack, you'll see that it is in fact a Zoroark. This is the only way you can capture Zoroark.
Besides, in order to obtain all three you'd need three separate games.