Galen Rowell and Joe Buissink I think are very reasonable examples of commercially successful photographers who like Adams turned a hobby into a successful vocation.
I believe that Rowell, Buissink, and Adams each have a couple very important things besides photography in common though. They are/were commercially astute to begin with and they each had/have passions/inspirations they wanted to share with the world.
These guys didn't start out to be visual artists. Adams was studying to be a pianist, Rowell was in the automotive business, Buissink was studying for a Phd in psychology.
Their artistic inspiration was driven by wanting to express/share their moments/experiences/emotions with others. Yosemite for Adams, climbing for Rowell, and emotions for Buissink. Photography in a sense for these guys was simply a convenient tool.
The important questions after the inspiration are present tense, like "what tools and skills do I need?" and "who is my competition?" not past tense, like "what would Stieglitz have done?".