Is it reasonable or at all possible to hunt upland birds and early ducks without a dog in September?

No idea about ducks.  You can certainly hunt sharpies without a dog, although you’ll be at a disadvantage.  Look for high ground and Buffalo berries.  You’ll bump birds.  Huns will be hard to find without a dog.  You can try forest grouse hunting at elevation.  You’ll kill a bird or two walking a logging trail without a dog.  No way I’d chase chukar without a dog.  

MT may close most of its public prairie land due to the drought though.