The Vbulletin Impex script has nothing to do with Photopost Information at all. This is where I think alot of the confusion lies. Your Photopost Information is in Photopost Tables. Impex is a script written by Jelsoft, Inc used for Importing Forum Data from over 80 forums into Jelsoft's vBulletin Forum Product. The script only concerns the steps necessary with importing UBB to vBulletin.
Your not going to migrate anything Photopost with Impex. The only thing you need to worry about with Photopost here is you need to upgrade your Photopst to the latest. After that you then take the documented steps I have outlined which have been noted in many threads on how to switch an integration since you have now changed to vbulletin. The whole upgrade process and switch integration steps should take you no more than 30 minutes.