Joining / Concat DNxHR HQ *without* re-encoding is it possible to precisely concatenate multiple DNxHR (HQ) videos into one without re-encoding?

It seems that ffmpeg can only handle MPEG streams.
As long as the streams have the same properties - resolution, pixel format, timebase, reference frame count, then they can be concatenated by ffmpeg. Strictly speaking, FFmpeg will concat non-matching streams, only throwing warnings for discontinuous timestamps in the input streams, but that output will not be accepted by most (or any) players.