The metadata in a DNG file is actually still XMP data (it can be stored in other formats too, such as exif). The difference is that it just gets recorded right into the DNG file itself rather than in a sidecar file. So, with DNG its the same story as the .xmp sidecar files, there’s still no edit history, collections info, flags, etc. That stuff only exists in the catalog – so back it up!
I have changed my opinion over time about converting everything to DNG. I used to do it to every photo, and sort of wish I hadn’t now.
I wrote up a little thing about why here if you’re interested.