Now that I think about it, individual instances of a MultiMesh don't get culled anyway. Even if fully transparent objects did get culled, they wouldn't be culled in a MultiMesh.
If I'm moving meshes with a shader, it might make more sense to move it nearer to the camera, so that grass is denser closer to the camera. But now that I'm using a spatial shader instead of a particles shader, is this a good idea? If so, what would be the most performance friendly way to do it? I could check the distance from the camera, then move that mesh based on the distance, but I don't know if that's a good method, or what the best way to implement that is.