So I sent FFG a note asking about Dori's response ability and if it can be used to absorb damage going to Beorn. The answer is yes:
Hi Paul,
Really glad to hear you're enjoying the Hobbit: Over Hill and Under Hill!
To answer your question: Yes, Dori can exhaust himself to take damage that would be assigned to Beorn. Dori's response targets the damage and not Beorn, so Beorn's immunity to player card effects is not a factor in this event.
Good question!
Caleb
This was mentioned as a possibility in an earlier thread, and maybe you all knew this, but now I do too! It is nice to know that there is some room for healing Beorn, in this response-type way and I think it will make him even more playable.
I can't think of any off the top of my head, but are there any other cards that have this type of response?
Paul