I second @Blanc 's assumption.
When I was still using Backblaze, restores lost metadata like Finder tags, but that applied to single files, like PDFs.
The image or even a regular Devonthink database backup should work without losing metadata of the files contained in that package.
However, I would certainly test it again in your case.
If you search the Backblaze subreddit, they are quite opinionated about not supporting metadata like Finder tags, because, according to them, they serve no good purpose (everybody should use folder hierarchies) and they claim Apple will not support them in the future anyway.
EDIT:
https://www.reddit.com/r/backblaze/comments/gwh3de/backblaze_metadata_support/
https://www.reddit.com/r/backblaze/comments/6vpidl/does_backblaze_fully_support_file_metadata/
https://www.reddit.com/r/backblaze/comments/3zd6z0/backblazeb2_and_osx_metadata/
https://www.reddit.com/r/backblaze/comments/dmbrya/is_support_for_backing_up_finder_tags_coming_to/
… Backblaze employee basically gaslighting users that there are no use cases for tags.
https://www.reddit.com/r/backblaze/comments/hoavox/how_does_backblaze_zip_the_restore_files_and_how/
… dmg and sparse bundle should work around the issue.