The world auto supply chain has become so integrated (March 18, 2011) that you are likely to find the same parts suppliers supplying to all auto plants. There was a time when Ford would frown at suppliers supplying to GM let alone Toyota. Today the world is a far different place , with suppliers supplying to everyone in their industry. In fact , you can be sure that suppliers who recently started supplying to the rejuvenated GM had to provide good references from other customers like Ford and Toyota.
[Note: This post from March 18,2011 was updated for formatting issues on May 22, 2021]