To be fair, there isn't a scintilla of evidence that they're involved with that. Some black hat is just using them as feedstock for content spinning. Happens to Wiki and my blog all the time.
Very possible. I gave more mention of that possibility in the writeup.
There are some weird things, too. I see what might be links between mystery numbers in the spam pages and parts of their URL, and I find it odd that they're the only site listed in those error messages, and there aren't a lot of those errors. Which may indicate that they're not deliberately blocking the spambots. But I will concede that it's weak evidence so far at best.
On another note, who is using your blog as feedstock? Can you give a URL to a spun copy of your stuff?
That's an error message from bots that are spamming random wikis. I wrote more about it here:
http://news.ycombinator.com/item?id=2215993