Converts vBulletin users to WordPress users.
It currently is not supported, this is only able to import users if WordPress is installed in the same database.
This currently doesn't copy users passwords to WordPress and check them there, it checks their password after grabbing it from the vBulletin user table. So, no but this isn't that hard to implement if you'd be interested in me adding this let me know.
No, it only copies users from vBulletin to WordPress. If someone were to register on the forums after doing the user import they would not have a WordPress account unless you ran the importer again. I don't recommend running the importer more than once. You should make a custom registration page and point both WordPress and vBulletin to that page. Which would then add their user data to both databases.