UniKey License Dongle doesn't appear to work correctly on RHEL63 guest on ESXi 4.1

According to this KB:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1021345

The UniKey STD licensing dongle should work under ESXi 4.1 in passthrough mode (it is currently connected to the ESXi server and exported to the guest via vSphere) and is certified.

However, though the dongle is recognized some of the time, I am seeing a lot of URB timeouts and general slowness when its connected.

What's interesting is that we see the SAME issue with ESXi 5 using USB 1.1/2.0 emulation. We don't see the issue with USB 3 (xhci) emulation on ESXi 5.

I turned on debugging on one instance of the issue and what's funny is I couldn't see the transactions pass by during UniKey_Find() (an internal API that looks for the presence of the dongle).

lsusb -v sees the dongle but its VERY VERY slow (seconds to return in some areas). We have one machine where it works fine but others where it completely fails. I'm not sure if this is actually the guests drivers or the hypervisor, but the problem seems sporadic.

Anyone use licensing dongles on Red Hat Enterprise Linux? Any luck getting them to consistently work?

Thanks!