Yes. I do believe that one can be a sadist without being a Dominant. I don't know how common it is...or maybe it's more common than I think.
A good question to answer before deciding that D/s isn't for you: how do you define "a D/s relationship"? There is definitely a wide variety of definitions - all the way from 24/7 D/s all the time to a couple who are vanilla in all ways except in the bedroom where the power-exchange comes into focus.