The point of a DNG file is not certainty that it's straight from camera or the other options you mention. The point is that it's a TIFF type file with all its parameters recorded in an industry agreed way. That's what makes it good for archival storage.
The original raw data in a DNG file is never altered. The DNG file is writable in certain segments, although not in the raw data segment. As such, with the correct tools, it should be possible to find what modifications, if any, has been made to a file. Certainly, people who work in the evidential image sector will be able to tell if a DNG file has been manipulated or not. This could be done by looking at factors such as whether they're looking at Raw DNG" or "Linear DNG" and other pointers, well beyond my understanding.
The whole point of DNG is to be a universally accessible raw format. I've yet to see evidence that the different parameters you mention cannot be found by people with the necessary skills. It's not an "elephant in the room" moment.
For more information about the DNG format and how it preserves it's original dataset without manipulation, see:
https://opencommons.uconn.edu/cgi/viewcontent.cgi?article=1027&context=libr_pubs
The Library of Congress only uses DNG format and, for many reasons, views it superior to all other proprietary (manufacturer based) raw formats. It's also the archival master format at The National Gallery of Art, Washington, D.C. It is, in short, the most trusted raw format there is and can operate without the input of any specific supplier's camera / system specific software.