Thank you both for such swift and helpful replies.
I'm very reassured that CodeRunner can, at least at a technical level, accept R code. I'm not sure exactly what my colleagues have in mind. We will be running on a server which also has my own STACK question type installed (https://github.com/maths/moodle-qtype_stack) and I think a combination of the normal Moodle questions, STACK and CodeRunner will be an interesting combination of tasks for students which combine mathematical and programming elements.
The 10^6$ question is always "What sort of question to you really want to ask?". I'll talk with colleagues about that one...