It could be sure if there are members whos accounts could not be found etc sure. Nothing is every fool proof when switching integrations.
You can do some searching with the individual user whom says he has the issue and see what the actual photos table is saying as to whom owns the photos.
If for instance they have another userid they should have another username and you can then look up that other username in
vb and see if they exist. The script can only update usernames it finds. The script used is here it was not something I wrote for you specifically.
Reassign userid's when switching integrations to VBulletin