Spots on tails, gum and body colours and head shapes are all good first glance indicators of species and should be all that is needed for identification but won't always be 100% accurate. As an example I have seen spots on the lower caudal on a few coho, especially wild fish, and also spots on the bodies and tails of sockeye. It does happen but not very often.
If you are fishing the Vedder and can't tell if the fish you have just landed is a coho or chinook after eliminating all the fish it can't be and using all the other indicators, get a little bit of the slime on your fingers and breathe deep
white chinooks, the stock most common in that system, generally have an unpleasant odour.