I have MY BLOG 3.0. I was using JomComment 3.0. The My Blog plug in is installed and functioning. All the comments imported without a problem. However the imported comments don't appear on the blog entries. Only new ones do.
If you display the blog entries using a com_content view (for example a menu item to display articles from category Blog, rather than a menu item to the My Blog component), all the comments appear, both new and imported.