unless you are using it for other things. Running VMware or Parallels, the USB handling is being passed off to the Windows system through the hypervisor, I believe. You would install the Windows driver for the device on the virtual machine. I have done this with a number of non-Mac supported devices, including serial port emulators. Keyspan does make the USA-28XG, which is a two port adapter (with mini DIN 8 plugs, so you would have to have the right cable). That is similar to the one I have. List price is high but maybe you could find one on Ebay, for example:
I'm not sure if there is a PC driver for that, so you would have to configure the serial port on the Mac OS side - that used to be possible in Parallels, but I haven't kept up with the latest developments.