How do I import existing products into Craft Commerce with the FeedMe or Import plugins?
Feed Me only supports Entries at this stage. Its on the short-term roadmap in allow importing into all Elements, including Commerce Products. This cannot be achieved through hooks at the moment. Keep an eye on the plugin page.

Update: FeedMe 2.0 now supports multiple entry types, including Commerce Products: http://sgroup.com.au/plugins/feedme/getting-started/introduction