I do and I love it. I have made regular, goats milk and soy milk yogurt soaps. I treat it like I would regular milk. I use the half and half method (half water with your lye..then half yogurt at trace).
I am sure there are more ways to do this, this is just what I do and works well for me. The soaps are so creamy and my skin loves it.
I also use Aloe juice instead of water. HTH