As it stands, if Jaso and Montero are the only catchers come opening day, I'll be disappointed. Firstly becuase Montero is a terrible catcher and secondly becuase either it means Jaso is riding bench while Montero catches, or they will both be starting with no catcher available on the bench.
In recent history, the list of players who have successfully been known as DH's only, is pretty short. And the list of those who were actually worth it over their career is even shorter.
I just don't think it's wise we hope for Montero to be as good as he would have to be to justify being a DH only player (or even a DH mainly and a bad backup catcher).