This is a hardware box, connected to your network, and a virtual USB driver installed on your virtual machine that allows it to use these dongles.
It's working fine, no problems with VMotion etc... only downside is that only one server can be connected at the same time to this box. So try to get as many of you licensing servers on a single virtual machine.
I've not yet implemented it, but Keyspan makes a box that can have multiple USB devices attached and multiple computers connecting to them. I have it on my desk but the application I was going to use it for has not yet been put in so I can't say if it works well or not....