ESX VMWare and USB port

VMWare GSX and workstation support USB hence those VMs support USB based dongles and devices.But ESX doest support USB hence its VMs dont support USB based dongles and devices.So you cannot map physical usb with the ESX based virtual machine (ie) guest machine.

Alternatives:
1.Consider LPT/Parallel port mapping.It is supported on ESX.Check esx25admin.pdf manual from vmware website.So LPT based Hardware Keys are better as of now.(Important:Now a days servers are coming with out LPT/Parallel ports.Be aware)
or
2.go for USB over IP options like USB over network http://www.usb-over-network.com/usb-over-network.html
3.Anywhere USB http://www.digi.com/products/usb/anywhereusb.jsp
or
4.go for physical server. :)