Rootstock is usually used for grafting. People buy rootstock and graft the varieties they want to the rootstock.
Dolgo is becoming popular with some folks as a rootstock for apple grafting. If it is true Dolgo it would make a Dolgo tree without grafting, and that would be okay if you want Dolgo. Bartlett is a fireblight magnet. I don't want a Bartlett Pear and I don't want Bartlett rootstock for grafting. It might be okay for grafting, but I personally don't want it after the research I've done on how rootstock can affect disease resistance.