I just published an new Arduino project on my web site that implements an DMX RDM Device using the DMXShield.
From the beginning the DMXSerial library was designed to send and receive DMX data packets. Now it is extended to support RDM packets as well. I had to overcome several pitfalls and stumbling blocks while extending the DMXSerial implementation and I will keep the current version because it needs only a very small amount of program data. The RDM extended version will be DMXSerial2.
What you can find in the attached zip file right now is an ARDUINO project including all the files you need to compile. Because it is still in WIP (work in progress) I did not extract the DMXSerial2 files into a library format yet.