Yes, they may have helped push the process along, but the church would have reformed on its own if no one had even messed with it, because all of its ideas would have been put out of date and they would have had no choice but to change it up.
I think that if a big entity like the Roman Catholic Church never has a reason to change, then it wouldn't change. I think that reform is usually influenced by outside sources having an impact. When dissidents are able to make something like the Roman Catholic Church reform, it is good for everybody and shows that times change and everybody needs to adapt for their own benefit.
No, the Roman Catholic Church would not have reformed on its own without the advocacy of dissidents like Martin Luther, because a dissident in one light is like a reformer in the other, so it is unfair to categorize reform of the Catholic Church in that way. In any event, the Catholic Church still hasn't reformed. My grandma ordered a papal blessing for her birthday. They just called it something else. Shipping and handling still applied.
The problem with any religion is that they demand obedience, and ridicule or ostracize any type of free thought. This is countermands any opportunity for reform or change in the absence of people who are willing to risk their own reputations, not to mention very often their lives, in order to point out fallacies, contradictions, and inaccuracies. Roman Catholicism, throughout history, has tended to try to hold onto traditions particularly hard, so I absolutely do not believe the Church would have reformed. Even today, I believe they would be perfectly happy if we still lived in the same conditions that were present in the Middle Ages.
Even with outspoken catalysts of change, the church is still slow to do so. The church also does not change simply on the whim of some people, but the protestant and lutheran movements both have had an effect on Catholocism. Regardless of what the catalysts may achieve, the church still is difficult. Even Catholic history shows the immovable whim of the system as overpowering not just people, or other religions, but Entire regions with multiple Nations answer the direction of the church.