The Bowyer's Bible Vol. 1 does have a few paragraphs on baleen. They considered it an "extinct" bow backing 'cuz let's face it, most people don't have access to it. Just guessing that the last time it was commonly used on bows was 70-80 years ago?
But they also wrote that master bowyer John Strunk had made bows with it, using it as a backer but also on the belly of another bow. Good luck and be sure to post pictures if you make one with baleen. I'd be interested just to see what the stuff looks like.