thankyou for your help. I tried that and it definitely worked on a 'static single image'. It didnt work on images I had converting in a batch process. Just cant get PS to 'hide' when it is batch processing...strange!
Ok, well that's as far as I can go. I have no idea what changes disabled hiding in Photoshop CC. Hopefully one of the staff can drop by and help.
I know this is a long time between OP and this reply so this is to help anyone else having the same problem.
The easiest solution I've found is to simply use OSX's "Spaces" virtual desktops and once you have the batch running open a new "desktop". this hides the active batch job in the original, now hidden, desktop.
to use spaces, hit the Spaces button (f3) and the + button in the top right side of the spaces bar to create a new desktop.
Note that if you want to access folders and other apps that are open in the same desktop as Photoshop you'll need to drag and drop them in to the new desktop space (hit Spaces key and literally drag the app windows from the desktop with photoshop open to the new desktop).
Once your finished hit the spaces key again and hover over the new desktop, now press the option key which will then show an X at the top left corner of each of the desktops, click on the new one and the apps and windows will "gather" in to the remaining virtual desktop