JJ, when you get a chance, would you please check which version of PM you're using?
I'm using 4.6.9 and all my IPTC data shows up in Photoshop, as inputed by batch ingest in PM. When I bring in my files from the memory card to the computer via PM, it renames all files, copies the files to my primary and backup storage, and inputs my IPTC data. I then use the PM interface to open the files in PS. I'm using PS CS6. The amount of IPTC data used is extensive.
The new upcoming version 5 of PM adds full support of the IPTC Extensions.