NI-IMAQ does not support third party frame grabbers because every frame grabber requires a board-level driver to communicate to the hardware (configure registers, handle data transfers, etc.). Therefore, every frame grabber manufacturer has a driver designed for their own hardware.
When NI-IMAQ is installed as part of VAS, application development support is added with LabVIEW VIs in the functions palette to interface with first party frame grabbers. These VIs do not constitute a driver, but they are wrappers for function calls to the NI-IMAQ driver. If you open up the IMAQ VIs at the lowest level, you will see that they consist of calls to the NI-IMAQ DLL, with some supporting code for error handling and other functionality.NI Vision Development Module (VDM) is a separate software set from VAS
and is an extensive library of LabVIEW image processing VIs. NI VDM can be used with images from an NI frame grabber, a third-party frame grabber, or from a file. The VDM VIs do require the images to be formatted into a proprietary data type called an IMAQ Image, which is the data type returned by NI-IMAQ. Other manufacture's frame grabbers often return an image as a 2-D array of data which can then be converted to the IMAQ Image format using the IMAQ ArrayToImage VI.