Someone with more in-depth knowledge can correct me, but how I see it:
python 2.5 has no "default" json module (unlike it's successors). Json can be obtained by installing python-simplejson. As such, it is NOT a part of the basic python installation.

So for that matter, it is not a standard package on the device (you can check yourself if it is installed) and not something for CSSU. I think a simple upload to extras-devel (see http://maemo.org/packages/view/python-simplejson/) is the way to go?