Dear Christopher
I checked a little the APO topic and found this one http://help.sap.com/saphelp_crm700_ehp02/helpdata/en/45/b858b0dbe5003ae10000000a11466f/content.htm
Definition here: Kits consist of a number of components. (in other term: there is a mterial having a BOM) and in SD / APO process the material can be placed
The DG, HSM etc. topic in EHS regarding such material is "interesting" and per company different business decisions come up. Interesting is that SAP provides "similar" solutions like "HU" Handling (which does have some "overlap" to the KIT definition) which are supported e.g in DG checks etc. (please check SAP online help if needed)
From legal point of view most companies try to do it like this:
a.) the kit is one material number and related to a REAL_SUB; the REAL_SUB does get a MSDS (because this material is sold to customer and therefore the MSDS must communicate anything regarding that material)
b.) second: many companies uses BOMBOS; the BOM items are once again material numbers; and therefore for "header material" using the BOM you can generate a BOS (based on BOM items) in EHS and then go on with further activities
c.) now regarding e.g. WM, eWM and other stuff: the BOM items are in most cases stored; therefore you need per BOM item as well a REAL_SUB to generate a "Hazardous material master" (check fo suitable storage location) ; the same is true in moste cases regarding DG as the BOM Items can be transported etc.
d.) now on Kit "header" there are many approaches to go on in DG topics. option one is: use the "worst" case of REAL_SUB in DG checks and on documents; or as you seems to plan, try to drill down per component; then execute DG check per component and then "collect" result to get DG block (or not).
e.) Label topic: In most case we are talking about EH&S product safety labels and DG labels as well; this is now "quite" tricky; as with "d.)" some companies print on DG label the "worst case" result; some other attach to the material the "material specific" DG label; the same is true with product safety related labels
In any case. This type of material gives rise normally to start a project to think about the different demands regarding that and to find solutions for that. The complexity of the procect to be started depends on the recent SAP landscape your are using
Some other similar issues can come up in EHS SVT as well (and if yo uuse SAP GTS you need to check further processes as well)
C.B.