If you grant access to someone's LiveJournal OpenID (or let the importer import your friends list for you), your friends will be able to access DW using their LJ OpenID and read your locked posts without needing to make a separate DW account. They will still have to come to DW and authenticate with OpenID, though: there's no way for them to read your DW locked posts on LJ. (Other than you crossposting the posts to LJ, I mean, but that does involve sending your posts to LJ, and a lot of people don't want to do that anymore.)