Admittedly, it's not enough to be fielded as a unit in their own right, but they always can be used with characters until their packmates are done.
A couple of people have asked me why I didn't go for the proper Fenrisian Wolves instead the Warhounds. While I love the proper wolves models, I went for these for a number of reasons:
1. They look more feral and brutal than the Fenrisian Wolves. These look more like barely controlled predators than their tamed and well groomed official counterparts
2. The background for my Great Company has them marooned in the Warp for a while. Whilst the Space Wolves can resist its effects due to the Canis Helix, their beast companions weren't so lucky. The Warhounds represent that.
3. They're cheaper. You get twice as many Warhounds for the same price as the Fenrisian Wolves
So there you have it. I might get round to painting the rest of their pack mates soon, but I feel the Wolf Priest and Grey Hunters calling out to me to be finished next, so you might have to wair