ESXi 5.1? EDIT: sorry, I didn't look at the screenshot very well :-) I did get USB working in 5.0 but 5.1 it stopped.
Exactly the issue I outline above. Looks like VMWare have removed USB passthrough support, frustratingly the GPU passthrough seemed much better.
I have given up on ESXi for now and am doing what I want in Xen instead. Have my Windows 7 VM working with my AMD 7750 and USB devices.