Elexol provides both a Virtual COM port and a DLL. On their Web site, they say "To operate the USBIO24 from within Visual Basic it is best to use the Microsoft MSComm control to access the COM port." While they don't mention LabVIEW, one could assume that they would also recommend using VISA to interact with their device using the appropriate COM (USB) port.
Are you an experienced LabVIEW developer? If so, doing this should not be difficult. If not, consult with the people writing the LabVIEW code that will be using these devices.
Bob Schor