I am experiencing the exact same problem.
I am using a Star Tech USB 3.0 PCI controller that I am trying to pass through to a VM runing Server 2008 R2 that is used as our Backup Exec Server. I want to attach external USB drives to be used as targets for off site storage. I have a call opened with VMWARE Technical support to help with the problem. If I find a solution, I'll keep you guys posted.