All this is doing is allowing you to do is vertex paint a mask that reveals a “blend” material across the verts of the meshes. We used similar techniques in Halo; we created “dirt skirts” using Houdini and Maya, then vertex painted the mask in maya. Once in engine you can just apply the material you want (i.e. sand) and since the vertex colors already export with your meshes, the material will automatically blend in with everything.
You can do the same thing in UE4. You can setup a material with 2 layers (i.e. rock and sand), then just paint vertex colors (in UE4, no need for maya) to mask which parts will be rock or sand, they will blend in and that’s that. If you want to get fancy, you can generate a mask in Substance Designer so it’s more realistic then vert colors, and get some more believable blending between the two objects.
I could do a tutorial showing both the vertex painting method and Substance, if people are interested?