Genuinely, a deal between Tumblr and Midjourney would be awful for Midjourney (and probably Tumblr, too, given the Likely Userbase Reaction) because Tumblr's tagging system is... idiosyncratic (and probably already included in the Common Crawl/LAION as image tags).
Also, if they're looking for, like, Licenced Art that they can freely use without worrying about lawsuits or whatever, Tumblr is full of uncredited reposts of stuff! It's one of the things it's known for!
you know that bit in Fern Gully whete the little tim curry sludge monster erotically sucks down industrial pollution amounts of toxins and turns into a gigantic orgasmic demon skeleton
first of all i just like replaying that scene in my head and second of all that's literally what will happen to any chatbot or picture generator loaded up with the incredibly hazardous output of tumblr.com