Posting to DW works and having it repeat in livejournal usually works provided that LJ isn't stuffed in some way, which seems to be more and more common. The trouble is that I have all of my icons here, get most of my comments here, have more friends here, etc. so always look at livejournal but rarely look at Dreamwidth unless there's a problem with livejournal.
I don't think LJ wants to acknowledge DW's existence, so no. As far as I can tell, there's only two ways to handle it: either post to DW and have it autopost the dupe to LJ (which is what I do most of the time); or post to LJ and run DW's copy engine periodically to dupe the entries and comments to DW (which is what I do to copy my flickr posts, since flickr also don't have a reblog link to DW).