Media Pro doesn't see DNG Ratings from Aperture?

I've tested a workflow for rating using PixelSync (www.pixelsyncapp.com) and Aperture. From Aperture, I can export the ratings via Metadata=>Export IPTC Metadata to Master, updating the original DNGs, and the ratings are seen immediately in Bridge. If I export the ratings as XMP (via Export Master IPTC4XMP), as a sidecar next to the original DNG, Media Pro still can see the ratings, as usual. But that defeats the purpose of the DNG and creating sidecars from Aperture requires a dialogue every time, choosing the location -- it cannot just drop a sidecar next to the original RAW or DNG. So is it a the problem with Media Pro?