I can not tell you what is correct for your server only you know that information.
To integrate photopost to the vbulletin users you need to install photopost to integrate with
vb. That is how it is done. You would answer all the information on install that is asked with the correct info.
If your existing photopost like I said has all the same usernames as the usernames on the forum you can
theoretically use the userfix script from the photopost import forum which you even commented about in your prior post to realign the photopost userid's to the new
vb userid's however as noted if the usernames are not found in
vb your photos and comments will be orphaned and owned by no one. This is not something we support I have made tools available to help switch integrations but by no means does every instance work.