Short answer from me is no.
A longer answer is that a long time ago I stuck one of those little temperature strips on the outside of the differential housing, it never saw more than about 50 degrees that was after a summer of trackdays - how that equates to the temperature inside the box I have no idea.
DonB did have a sensor in his differential to measure the temperatures but the engine failed shortly after and I'm not sure if any usable data was recorded.
Now that I have my DL1 datalogger I plan to in the not too distant future to run a sensor in their myself and see what happens.