Dear Chris
I can not go intodetails but please cehck EHS DG customizing. You will find an activity in which the mapping is done (EHS product safety structure/data to DG data); by enlarging you should be able to get the data filled.
Check may be these links:
http://help.sap.com/saphelp_46c/helpdata/es/b0/1b4b6e5733d1118b3f0060b03ca329/content.htm
Enhancement of the Dangerous Goods Master - Dangerous Goods Management (EHS-DGP) - SAP Library
Incorrect assgnt of dang.gds user-defined texts of real sub.
Spec.features for filling dangerous goods user-defined texts
I am sorry to say that there is no consulting OSS note available regarding DG filling.
Hope this helps
C.B.