The API is there.
As for the incomplete products, you can drill them down by status if you want to help complete them.
You can pick and choose from http://world.openfoodfacts.org/states
The API seems extremely limited. It seems you can find product info based on barcode or something, but there doesn't seem any way to submit products using an API. Of course with scraping one could "fake" and API, but that kind of sucks ...
For instance, here are the US products with photos selected, but still in need of nutrition info: http://us.openfoodfacts.org/state/photos-validated/state/nut...