I don't see a need for such integration. Why don't keep it separated?
As an alternative to vB, you could migrate to PunBB, IPB or phpBB as these are supported by DokuWiki. It's perfectly possible to write an own plugin for vB and judging from the available ones, it actually doesn't require much effort.
PunBB:
http://www.punres.org/viewtopic.php?id=319
http://www.punbb.fr/aide/doku.php/in...ite?s=dokuwiki
phpBB:
http://www.dokuwiki.org/tips:integrate_with_phpbb
http://www.dokuwiki.org/tips:integrate_with_phpbb3
IPB:
http://www.dokuwiki.org/tips:integration_with_ipb_2.x