I dont really understand your question. If your asking if you can save a rom to a usb drive, and play it on a computer, then I think the answer is yes. I dont see why it wont work. Even better save a emulator and the files on the usb drive so that you dont need to install the emulator.
But I think you will need to copy them to the computer once the usb drive is in. I dont think the emulator can be played from a usb drive.