I don't think BMW "certified" Dinan but I do know a lot of US BMW dealers are also Dinan dealers which doesn't imply the certification from BMW corporate.

With regards to the factory warranty, it's still valid unless they can prove that your mod was directly responsible for failure of an OEM part. However, Dinan's warranty covers their parts as well as any OEM parts that failed from their products and their warranty is usually for the same term as your BMW warranty. So in essence, you are covered by either manufacturer.