I use IMatch since several years. Writes/reads IPTC/XMP to/from the NEF. The NEF can still be opened by ViewNX2, CNx2, ASP... Maybe not by Adobe products who anyway write only to sidecar XMP.
I do renaming, culling and most of IPTC editing in PM5. PM5 writes to the NEF, this info is directly accessed in the NEF by IMatch
The next release of Imatch, IM5, is now in public beta test (you have to be a registered Imatch user to downnload it).
Francis