In-game it really doens't matter.
You can run along with a special Azumarill and still beat the game. I beat my whole BW2 Elite Four with a team of Caterpies and Weedles once.
On the competitive side of battling (which I think you meant) though:
Of course it is, on the 3DS that is.
However, if you plan on battling with Showdown! or something like that, then there is no need to breed.
Here are the benefits of breeding:
- You get to put some awesome moves on your Pokemon. Like Ice Fang you mentioned.
- You can get some good IVs on your Pokemon to make them more efficient. See more here.
- You can Masuda Method for a shiny Pokemon. (optional)
The best way to get Ice Fang onto your Luxray would be to breed a male Arbok with Ice Fang (learned through Move Relearner) to your female Luxray. Other than Arbok, you can also use these Pokemon (remember, all must have that move and be male):
Hope I helped!