what ?
it seems you are mixing terms that have nothing in common ..
first of all ManyCam is your camsplitter software - so it has no influence on what kind of shows you do. Never heard of a problem when using a splitter instead the "pure" webcamdriver. Only thing what can happen is quality of the splitter is lower than original cam.
second .. under "Flash drive" i understand kind of a USB Memory Drive or maybe a SSD - and that part make no sense to me.
third .. never belive what a customer says about your hardwareand how things work ..
so just to be clear - if mfc don´t want that you use a Camsplitter - you wouldn´t get any picture in mfc - and at the end mfc would hurt themself because - you earn no money - they earn no money.
If you work a lot on mfc - it is helpful to have a customeraccount with some credits on it - just in case to make a quick test - to be sure things work how they should.