Hello,
Well, the nice thing about Grasshopper is that you can implement your custom algorithms for e.g. importing G-code and turning 3 or 5-axis toolpaths into proper robot code.
At the moment, we have a component for SprutCAM, but a while ago we also worked on a postprocessor for VisualMill G-code (which should be similar to RhinoCAM). So it's definitely possible. The first step would be to send me an exemplary G-code file. If you can choose from multiple internal postprocessors, choose the one that makes the least messy code. Then I'll be able to tell you if that is easy to do or not!
Best,
Johannes