Yep, they probably consider Hep C a "major medical condition". On the bright side, I don't think employer provided coverage can exclude you based on pre-existing conditions.
I was able to get long-term disability insurance a few years ago during an open enrollment period, in spite of having Hep C. I can't remember if they asked health questions, but during that particular enrollment time, my company was changing to a new disability insurance company and we could be insured regardless of pre-existing conditions.
If pre-existing conditions are considered in your "open-enrollment" period, you will probably be denied coverage, but you can't lie and say that you don't have a major medical condition. If you do, and you ever have to file for the disability insurance (even if your disability is unrelated to Hep C) they can say that you were untruthful on your application and deny payment of your claim.
I would certainly say number two applies as it can be a life treatening chronic condition and if left untreated it can lead to many other problems (cirrhosis, transplantation, autoimmune disease etc.)
Number 3 I think they mean blood disease like a cancerous blood disease - this is a liver disease although the virus ends up in your blood it's really all about the liver and it's complications from the virus.
that's my GUESS.