Yes, they are. Although some people think Mormonism is in its own category called "Restorationism," churches which believe they are "restoring" the "true" church after all the others have wavered from the original teachings.
Congregationalist, yes. Quakers -- well, more or less yes, but I doubt whether the Friends themselves would agree. Latter-Day Saints is a wholly different religion with its own distinct revelation, its own 'Bible' and its own prophets. It is to Christianity what Christianity itself is to Judaism -- in my opinion. Not a denomination, but a major schism.
Congregationalists and Quakers would be Protestant.
The Church Of Jesus Christ Of Latter Day Saints is the same church that Jesus Christ started when he was performing miracles and starting the Christian Church during his three year ministry.
So in that sense, the Catholic Church is Protestant, at least from the point of view of Mormonism.
Since the Catholics broke off from the True Church Of Jesus Christ, the moment that they were formed by the Roman Emperor long after Jesus Christ was crucified and all the Apostles had been martyred or had died of old age, or were not available, then they themselves were never the true Church Of Jesus Christ to begin with.
Catholicism was merely a collection of pagan beliefs mixed with certain sometimes odd interpretations of what the Apostles of Jesus Christ taught the people of the Roman empire over the years. Not Christian, at least not completely.
As a result, any Protestant Church that broke off from the Catholic Church can be seen to clearly to be coming from the same trunk of paganism, and as such are merely a branch of Heathenism, and as such cannot be THE true Christian Church.
So The Church Of Jesus Christ Of Latter Day Saints is the one true church, as such it is not Protestant. All other so called Christian Churches are Protestant to Mormonism, is the way Mormons think of it.
Mormons belong to the same Church that Jesus Christ organized.
Any one desiring to know the truth of this assertion, can read The Book Of Mormon (The Second Witness Of Christ), pray about whether this book is true, with a sincere heart, and they will most certainly receive the answer that it is THE true Church Of Christ.
Simple as that. As long as you are living the commandments, you will receive the truth plain as day, clear as a bell.
If you would like more information on this and any other topic of LDS theology, contact your local LDS missionaries, and they will be happy to come to your home and answer any question that you have. Heaven, and Representatives of Jesus Christ, are just a phone call away.