If your cat is not strictly an indoor cat, you can be assured that it hunts even if you don't think so. Most cats will hunt and eat some of it's kill, because that's their nature.
I suppose cats go thru some detox also, so if the raw food made them sick, it might have been detox. You could try another brand.
If you want you can make your own raw foods for the cat. I gave my cats raw chicken, some livers and hearts on occassion, and they loved it. That was years after eating standard cat diet of packaged and canned foods. They did hunt though, and I know that because I would find their kills sometimes, and one I could watch as he laid in wait at vole holes.