In the Aussie military system while I was involved (not recently, only up to about '95) our touchdown autos - and there were lots of them - were done almost exclusively to grass.
You would always check it out first so you didn't use anything too spongy, and it was very kind on the skids and pretty straightforward. Firm, dry, shortish grass is good.
I heard of a few problems where guys ended up rocking forward on the toes when the skids dug in on softer grass, but in general it worked very well.
This was Hueys and Squirrels, and I know the Kiowa guys did it too.