I've been chatting with a friend and expert on these things (Dr. Meredith Evans) this weekend and he doubts that there was any collaboration between Llew Tegid and Graves BUT Ll.T. and J. Lloyd Williams, founder of the Welsh Folk Song Society amongst other things, collaborated on a number of folk music projects. Graves was in contact with Williams and often asked him for prose translations of Welsh songs, which Graves would then versify. I'm not saying that this definitely happened with Hunting the Hare, but it may have been one example...

sian