The wiispeak mic is a usb input while your pc mic is a standard headphone jack size. The wii has drivers to support the wiispeak and the wii does not have a mic jack plugin.
In order for the wii to pick up a PC gamepad controller it would have the drivers to support the device. The Wii does not have these drivers by design, they want you to use their controllers. The question is, COULD someone program the drivers for a pc gamepad to be played through the wii... Possibility, but a classic controller is $20 and very functional. Just buy a classic controller.