That's the way it works indeed. I use that method a lot with the internal grass too, being careful to mask out any gravel areas (grey grass).
So to reiterate for newbies: indeed add a transform shader in your object parts area, set to world space and get the shader into its input by rightclick and find the grass shader from the popup menu. Often it is easy to begin its name by an A or 1, so it's on top of the list.
But making it really fit needs some extra work. Mostly they end up too dark, so I up the default color in the object part(s) to a number between 1.2 and 1.5. You can decrease the opacity to 0.7, and set translucency and reflection to kind of fit. Depends also on whether you have any Lambert shader or reflections in the original grass shader clip.