First reproduce the orphaned record in the vB database (per this post). Here is the orphaned record in vB's moderator table:
Then import to xF. Here is the corresponding imported record in xF's xf_moderator_content table:
You can see it imports the orphaned vB super moderator as a xF content moderator, but without any content assigned to him. You can see this in the Admin CP:
Admin CP -> Users -> Moderators
It shouldn't import the orphaned moderator at all.