Links 3 integrates reasonably well with vBulletin forums. The user authentication uses the vBulletin system, but the user table in Links is still used for adding links, newsletter etc. It gets a little bit cumbersome but it works ok.
There are portal add-ons for vBulletin that should also work fine with Links.
There are portal add-ons for vBulletin that should also work fine with Links.