Here are some redirect scripts that you can use following an import to xenForo. These scripts should work in conjunction with your vBSEO rewrite rules. I don't think you need to do anything special to get this working. It should redirect your vBSEO URLs to the new xenForo URLs.
xenForo has its own friendly URLs which are being used here on this forum.
Redirects for vBSEO'd URLs Works perfectly with vB 3.8 - 4.x versions. If you are using vBSeo custom rewrite rules I suggest it. I was using vB 3.8 and redirected all links perfectly. It also works with vB 4.x. Kier released a new version of the redirection script which allows forums to be moved to subforums.