I believe they are not one and the same.

Green Supply chain engineering practices are often developed by companies to cater the needs of many of their manufacturing partners, not just for one company or a single OEM. They are often internal practices (governing  best practices) to make their organization and process efficient cost effective and make them viable for running their business/ operation efficiently and more competitively.

Green supply chain management practices are often developed by OEM or business partners-- often independent of any supply chain involvements in order to keep neutrality with other supply chains. It is targeted towards meeting major needs of the OEMs not for any particular supply chain.

If you are saying that why they do not work together so that the resulting practices meet the needs of the both organizations (supply chains and OEMs), I believe it is a good idea. However, that type of collaboration often locks them (OEMs) up – for instance makes that particular supply chain one of its (OEM) business partner.

OEM will have hard time changing supply-chain in the midst, or for shopping around for the best one, they could find in open market.  

Hope this helps distinguish the two.

Thanks

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