Supersonic tip speeds are not a fatal show stopper. They increase noise quite a bit. Maybe that explains the characteristic noise of the Bear.
A propeller blade is like a wing: it produces lift and induced drag. Like a normal wing it has a critical Mach number. If it approaches that Mach number or exceeds it, the drag increases dramatically. So the overall prop efficiency goes south. However, the tip of the propeller blade only contributes its part, the majority of thrust is produced more inward.
Actually, there was an aircraft with a "supersonic" propeller. It is supposed to be the noisiest aircraft ever!
Republic XF-84H - Wikipedia, the free encyclopedia