Is it ethical/ correct to cite a confidential document/ paper (under NDA)? Each paper should be able to provide enough evidence that its claims are correct. Nowadays, where the number of joint industry-university projects grows exponentially, many confidential documents produced by private companies become available to researchers in academia under Non Disclosure Agreements (NDA). 

My question is the following: is it ethical to cite a confidential work in a scientific paper and use it to make some statements, while the rest of the scientific community cannot evaluate the accuracy of the claims in that source? 

In my personal opinion, this type of reference should be prohibited, since it hinders the progress of science, but I would be glad to hear other opinions on this topic and especially how they believe that such a case should be treated.
If the information you want to disclose is contained in a document that is covered under a non-disclosure agreement with the industry partner, you will need to get their written permission to disclose the content that you're referencing at the very least. If I were reviewing your article, and this reference were key, and the company had never published this document, I would be inclined to make negative comments in my review about the lack of publication of a key reference which might lead to the rejection of your article. You might have to work hard to convince your industry partner to either publish the information from the confidential document in a separate, smaller format, or to publish the confidential document in its entirety in order to get your article published. 

Either way, if you rely on NDA materials, you still have to cite them. It'll be best for your publication chances if the company discloses this information itself before you try to publish. Otherwise, even submitting your work to a journal or conference will require permission from the company since submission will count as disclosure.