Are you using the NI-IMAQ for USB functions or are you calling the QuickUSB libraries from LabVIEW? Unless the USB camera is DirectShow compliant, then it will not work with the NI-IMAQ for USB driver. You can use the Code Interface Node in LabVIEW to call external dll's, and it looks like from QuickUSB's website that is the best way to go. Hope this helps.
Jason N