I cannot answer your question about VISA and USB. I would assume the answer is "yes" because I do not see why that wouldn't be the case. However, all the USB devices I have ever used came with some device driver and most of the time I could just use the device driver's functions directly in LabVIEW. That way if the manufacturer updates their driver package, you can take advantage of it in your own software in a modular way.
If a driver is available (like a .dll), then I would first try to use the "Call Library Function" in LabVIEW to access its methods. You will most likely need the documentation for the driver. If the inputs/outputs for the driver's function are complex, then you will need to write a wrapper .DLL in C or something to make the function calls more accessable to LabVIEW (which seems to only be good at simple data types when using the Call Library Function).
-nic
