I think it's rare to see JSON HyperMedia data formats in the wild, XML seems the preferred choice due to its use of attributes for metadata annotation.
That won't work reliably with relative links. It also lacks any kind of link annotation (so, is this linked resource a "parent"? A "child"? Metadata? And so on).
Here's on of the few examples I've found that uses JSON: http://restafari.blogspot.com/2010/10/evolving-hal.html