Changing the extension was the first thing I tried, but ended up with double extension - .dng.tif and win 7 would not let me delete the .tif bit.
ReName master should do the trick; good for a whole batch.
http://www.joejoesoft.com/vcms/108/I've tried out RescuePro again, a later version and it found CR2 raw files with the correct extension.
I suspect if you ask your recovery program to recover "photos", it may not recognize raw extensions and therefore extract the embedded jpeg's, including any thumbs. Try recovering just "files" if that is possible.
I've also tried re-naming a .CR2 file to .tiff and back again, no problem. W7 asks if you really want to do that and I said yes.
Terry