I mean DNG as generally used in the photographic community. What makes something a DNG is that it follows the DNG/TIFF structure and tags, not that the pixel data is untouched sensor data, so in that sense, you are correct. In fact, the spec already allows JPEG-based compression for the image data, and Adobe uses this in things like lossy DNG whwere the pixel data is JPEG-compressed and nothing else.
OTOH, if that “JPEG” is just an 8-bit, tone-mapped, display-referred image, then wrapping it in a DNG container does not make it raw again, nor make it adjustable and mostly defeats the point of using DNG. It would be a valid DNG strictly as a file format, but a pretty pointless one for photography.