Yes... upper-upper Sheep Creek with canyon run is runnable -- but -- only by very skilled experts with a high level of endurance and routine practice having the right equipment.
I was the first documented raft decent of the upper reaches of Sheep years ago. It is runable by raft and canoe or (better) Kayak. Upper Sheep is quite steeeeep water and technical --- some 4-legged "boulders" will move (Bears are everywhere!!!) struggling in the very swift current. Note that the Put-in is very demanding --- not suggested come mid summer or fall.
This is also a flyweight trip as far as extra equipment... bare essentials & you need self-rescue swiftwater gear plus wet or drysuits. Huge fish up there, but plan on 100-120 pound line to land them in pockets - if that. The flow will knock you down if you wade knee deep! Hunting anything other than maybe Brown Bear would become a foolish hunting expediture - very high concentrations!!!