Your actually in luck!
In Most cases you would be out of luck because its not really a problem with our software or our importer. You choose not to have those two application integrated so userid's would not be correct as you have found out.
Now enough people switched integrations to vbulletin that I wrote a little tool for that here Reassign userid's when switching integrations to VBulletin
It was essentially written to realign photo id's after people imported phpbb2 to vbulletin etc but it works really for anything. What it does is grabs the photo username and authenticates the user against vb
and grabs their info and updates the userid with whats in vbulletin or really any forum you integrate with.