I will take a stab at it. The short answer is "no". A GPIB device is not a "COM" port and cannot look to the OS just like a serial port. There are fundamental differences which is why GPIB is so much better than a serial port. To translate this into NI terms, to make this device available to VISA for use, one would have to create a "Passport" file. These are part of the VISA infrastructure and connect VISA to hardware. However, NI does not make the API for Passports public, thus it is impossible for any third party to create a Passport. That being said, for some reason HP has a passport created to talk to their PCI-GPIB card!
Creation of this passport is probably non-trivial and this is why NI has not created a passport for their USB-GPIB or their Firewire-GPIB devices. The actual connection to the hardware for USB and Firewire is relatively trivial for the Mac OS X.
The device you mention probably has a USB kernel extension to handle calls to the hardware and a Framework for programs in user space to call it. The LabVIEW connection is relatively easy with the "Call Library" function to the Framework provided by the vendor. But you will have a hardware specific program and cannot take advantage of various features of VISA.
I did this for my PCI-GPIB driver before NI got around to finishing theirs. I made a bunch of "VISA-Like" VIs but they were not VISA and thus the programs became hardware specific.
If the vendor will give enough specifications for their USB-GPIB device, VISA could be used to access the RAW USB data. This is a bit tricky and not well documented at all.
In summary, GPIB is not a COM port and that device will not work as well as a native VISA implementation. But since NI has not created such an implementation it may be the way to go.
-Scott