Korg has never been owned by Yamaha. Several years ago, Yamaha's President loaned Korg's president, who are good friends, some money to grow the company larger. This loan was repaid and there is no connection other than friends. Korg does buy Yamaha made key beds for use in some Korg models. Just as many companys use Fatar made key beds in their keyboards.
George Kaye
Kaye's Music Scene
Reseda, California