I made the same reply on another thread,
https://discourse.mcneel.com/t/how-to-show-curves-and-points-in-rendered-and-or-arctic-mode/56227/9
but I thought others might find this workaround helpful,
I know this topic is old, but I just ran into the same issue of rendering curves from GH as an animation (this makes it impossible for me to bake and set a layer material for every frame. the Human plugin has a custom line weight setting which converts lines into meshes so that they can be seen in the rendered viewport. https://www.food4rhino.com/app/human