@krass - I'm not sure how it works in V-Ray, but in Rayscaper, the grass creates a scatter behind the scenes on the surface and then assigns UVs so your textures also work on the grass surface. We have some hard-coded grass patches in the software. The density limit is there for performance reasons; making it too dense could crash your GPU if it's not beefy enough, so there's a limit.
Way back, when I was a developer on the OctaneRender team, we implemented hair and fur using special hair "geometry," which is like tiny strings of geometry next to your normal triangles. I can also look at this method in Rayscaper. It's a bit of work, so I can't really promise this in the 1.0 release (which I wanna get out, because people think Rayscaper is crap because it's still in beta).
edit: I'll increase the density limit a bit in the next release anyway, then you are unblocked for creating carpets until we have something better.