I think technically, yes, it would be possible to spread Hep C if the cat scratched someone who had Hep C (and drew blood) and then scratched someone else (and drew blood). I doubt it is very common. In fact, I think it is probably very uncommon.
However, if you are worried, then talk to your doctor and get tested for Hepatitis C.
This is an interesting question and I hope some others chime in. They don't know everything there is to know about transmission but any blood to blood contact is a risk factor. I am now wondering about my moms cats. She doesn't cut their nails and one got hooked in my hand last week.