After the cnic_register message is stuck on the console, you still need to wait a few minutes for ESXi to finish booting; there will be no indication of progress. The handoff of pcie control is somewhere in the middle of the bootup procedure. When the card is passed to a guest, the guest takes over the card when powered on and replaces the frozen console screen
Don't know if you've done this or not, but I had to be careful of which host usb controllers I selected for passthrough to VMs. It seems ESXi doesn't like it too much when you passthrough the port that its flash drive is connected to 
. I think I had to reinstall ESXi and reconfigure the host after that one. Haha. Now that I have all the "unknown" devices mapped to the corresponding ID, that shouldn't be a problem