Everything is in the title. just adding more characters to reach the 30 characters mark.
I could not find one. There was conkygooglereader
but the Google service has ceased.
conky indeed is used for system monitoring such as CPU, HDD, system messages , etc... So I don't think you could find a rss reader.
Instead you can use a similar approach called screenlets.
creenlets are small owner-drawn applications (written in Python) that can be described as "the virtual representation of things lying/standing around on your desk". Sticky notes, clocks, rulers, ... the possibilities are endless.
You can find multiple kings and types from http://gnome-look.org/?xcontentmode=6700.
Now back to what you want. First add the screenlets repository:
sudo add-apt-repository ppa:screenlets/ppa
sudo apt-get update
Now you can install a rss reader called feedreader-screenlet
sudo apt-get install feedreader-screenlet