I wouldn't be comfortable using any subsonic .300 BLK round as a reliably humane hunting load for anything farther than a 10 yard head shot- but that's just me (haven't hunted for decades). For quietly dispatching two-legged predators, though- something like the Lehigh 194gr Maximum Expansion round should be quite effective at its job.
Both light and medium weight supersonic loadings in .300 BLK, however, have proven themselves to be very effective as hunting rounds within their intended ranges- performing ballistically similar to .30-30 Win (which has arguably put more meat on American dinner tables than any round in history).