A couple of scripts in the other forum for moving data lines back and forth between OmniGraphSketcher and OmniGraffle:
http://forums.omnigroup.com/showthread.php?t=22619
http://forums.omnigroup.com/showthread.php?t=22622
http://forums.omnigroup.com/showthread.php?t=22619
http://forums.omnigroup.com/showthread.php?t=22622