I have read many offerings from individuals that make there living from their writing, and I can say they weren't all professional. I have also read offerings from people whom I would say were just doing it for relaxation, or fun, or to express themselves and find it professionally produced. So I may need to dig into your question a little.
If you are asking if someone only writes for the cathartic value, even though they may actually pick up some coin along the way at HubPages, does that make them a professional writer? You see, the way you framed your question matters.
A professional baseball player, a professional football player, and a professional basketball player walk into a bar....the beginnings of a good joke maybe. But keep in mind, you may be able to differentiate these people against others who play baseball, football and basketball beyond the fact that they get paid, right? Because they are really, really good at what they do. What is the difference between these professionals and a professional writer, aside from some level of athletic performance?
If you are considering writing professionally, I suggest short stories, articles for magazines of specific genre', or trade publications where you can get practice. Become knowledgeable of something better than most others and tell people about it. If it is food, divide that down to one course, main, appetizer, desert, drinks, and know it better than anyone - and write so I want to eat the page and will get fat doing it.
That's my shot at an answer, I hope it helps!