That's an interesting question.
As an experiment, I just downloaded this book
三字經 in EPUB format onto my Sony Reader. I just picked the first one I found at the Gutenberg site.
My reader displays it as all question marks:
?????????.
I can't read Chinese, but I can view the document in my Firefox browser with the
EPUBReader add-on, and I can see Chinese characters, so I believe the format is good. I just can't read it on my Sony Reader. I don't know about the Kobo.