My general rule is; What do dogs do naturally without human influence? Unless they are climbing a mountain, dogs wouldn't really encounter exercise that works the body the way climbing stairs does. Tough to get physical exercise in the house. I have a large carpeted basement I let the dogs play in and wrestle in when the it is raining or the weather is too poopy to be out in the yard.
I'd personally say no to the dogs running up and down stairs for exercise. If you can find a treadmill that might be a better option. The dog would have to be conditioned to use a treadmill safely, of course...