I've just tried to import my DotClear blog into WordPress and it went find, but there are some permalinks backward imcompatibilies.
Dotclear uses a permalink URL like:
During the import, WordPress re-created all posts and affect a new id to them, this makes all referenced permalinks invalid since %post_id% isn't the same.
If WP keeps the same id for each post, old and new URL will match and referenced links to permalinks won't be broke.
All the best,