There's a really good post about dgs on highend3D.com in the forums. Link: https://www.highend3d.com/boards/inde...owtopic=158994

Now to use a dgs first go to your hypershade. Right above your material selection there's a button saying "Create Maya Nodes". Click on it and choose "Create Mental Ray Nodes". If this option doesn't show make sure Mental ray is loaded. (window>>settings/preferences>>plug-in manager and check loaded next to "Mayatomr.mll")

The material on the very top of the list is a dgs

Hope that helped