After looking at the phpBB 2.0.3 -> 2.0.4 upgrade script, it looks like the mySQL schema (layout) doesn't change much. The changes that are made would not be affect the importer (I hope). All that is changed is the search match, user, and prune tables. The user table would be the only one I would be worried about, and the changes that were made are just changing the default row values.
So it should work fine, unless I missed something