Okay, I set up aMember 4, installed the vBulletin plugin and it all seems to be integrated. I set up a test user and it is showing as a user in aMember, but not in vBulletin. I tried rebuilding the vBulletin database and that didn't help. Kind of stymied and nothing I find online is helping me figure it out.
Did you setup integrations protection ? amember CP -> Protect Content -> Integratios -> New ? on above screen you need to assign vBulletin group to aMember products.