OK. Some updates to my previous post. Turns out it does work, but there are some issues regarding either the vsphere client and/or vcenter. I made the changes in my previous post from a vcenter server (the latest version). When I logged into the host directly instead of going through vcenter it showed that the USB 3 controller was indeed marked as a PCI passthrough device even though at the same time the vsphere client connected to vcenter was still showing the above behavior. After rebooting the system the USB 3 controller was available for for VMs, but the configuration screen, both in a vcenter connected vsphere client and a directly connected vsphere client showed that a reboot was still necessary to use the device. However, when I brought up the VM it was able to use the USB 3 controller anyway. Also, if I opened the dialog box for the PCI Pass through devices it showed as not being checked even though it was usable. If I check it again and hit OK (note that it's currently in use by a running VM), it stilll shows as needing a reboot for about 20 seconds and then suddenly changed to showing a normal status. I tried bringing up the vcenter web client and in that client the device showed a correct status (before I did the above with the vsphere vcenter connected client).
It looks like there are some presentation issues with either vcenter, the vsphere client, or both.
Now for the good news. Every test I've run with the USB 3 controller inside the VM has worked just fine I've connected and disconnected hard drives and a card reader with a camara flash card in it, and they all work just fine in the VM. I also tried moving the USB 3 controller to a WinXP VM and it worked there as long as I set "pciPassthru0.msiEnabled" to "False", which was the same behavior as in the previous version. One thing you should do first before you upgrade from 5.0 to 5.1 is to remove the USB 3 controller from the VM using it because, at least in my case, the controller was identified differently than it was under 5.0, so if you leave it in the VM from 5.0 it shows up as a non-existent device and you have to remove and re-install it anyway. I also noticed that version 5.1 seems to do a better job in correctly identifying the devices on the PCI bus. Under 5.0 there were a couple of devices showing as unknown, which were the built-in combo USB controllers (I'm using an add-in USB 3 controller because under 5.0 I couldn't seperate out the two on board usb controllers without eliminating the ability to connect a keyboard and mouse to the host, although since they are now both identified I might be able to under 5.1, but I haven't tested that yet).