You have a number of issues you're umping together.
1. Snapshots in Lightroom/ACR. Snapshots are written to metadata, so they are portable. WHile it's not in ACR, a Bridge script we have will enable this:http://damuseful.com/movies/snapper.mov
The DNG spec does not really need to support this, since it' really about the XMP syntax as defined by the raw processor.
2. The DNG spec does, however, now provide for multiple previews to be embedded into the file (although no one does it yet). This would enable previews from multiple applications, as well as multiple versions from one application. The name as part of the DNG spec is soething that needs to be ther to help tie the particular settings to a particular preview.
3. Since Aperture does not own the ACR rendering engine, it wil never be able to reproduce ACR renderings using the instructions - it's just not possible to wire this up. It *can*, in theory, make use of the embedded rendering to give the user access to the ACR work. They just have not enabled robust use of the preview yet.
4. Snapshots predated the new DNG spec, since they are ACR specs, not DNG-spec related.
5. LR 1.4.1 and ACR 4.41 both started making DNG spec 1.2 compliant DNG files.