I know vbagallery could handle a gallery like yours. I am sure Brian who makes it could work with you on any importation concerns but onto the topic at hand....
Can you share some of what you've done for the wrapper? I mean if its just getting it to appear in a vb page, that in itself shouldnt be hard. Try taking a look at this tutorial on creating a vb powered page. Essentially its the basics that you would use in any custom coded vbulletin powered page.
https://vborg.vbsupport.ru/showthread.php?t=62164
You may want to also take a look at the global.php file.
I think some other threads were recently posted about passing session info that you might want to look at. You could probably modify the vb log in file to set a cookie for the gallery which might also help but I am not sure how you would sync the two user systems via thier embedder how it would run off the vb user tables.
Looking at it from that perspective, what does vb need to tell gallery in what format?