The only 5.1 build where it seems to work at least for one reboot is 1021289 (the last Patch before Update 1), Otherwise the only option is to go back to 5.0, there it's working with all builds.
Our call at vmware has been closed. They confirmed the problem and that for our case none of the available workarounds (normal USB device forwarding or using a Network-USB-Server) would work, since the USB-Dongle we need to use inside the VM for a banking software, doesn't work when using this workarounds.
Using USB-Servers is always our first approach, since there we're not bound to the host hardware and can use vmotion. Using USB device forwarding and USB Hostcontroller Passthrough is always our last resort. For us performance is not that important as for other users in this thread using it for USB3-Hostcontrollers for Backups...
There is now a KB-Article http://kb.vmware.com/kb/2044963 regarding this issue.
I'll say it this way, vmware-Engineering was kind of surprised, that it even worked in ESXi 5.0. They continue to investigate for a fix for this issue, and maybe they've already identified the cause, but it'll be not available before Q4/2013 at the earliest, and even that's not for sure if they encounter any problems during testing.
So currently there's no other real solution than staying with ESXi 5.0 if you need USB-Hostcontroller Passthrough.
Maybe it helps to push the priority for this fix if other members here with active support contracts could also open a case with vmware.
