As someone who has done this for the last 10 years, my two cents:
Questions:
1. Can an individual work full time as a in-house medical biller for a hospital/provider's office and work part time as a freelance medical biller on the side successfully?
Yes, but be prepared to work 7 days a week, 365 days a year, depending on the situation/volume of the freelance medical billing side of things. When I started doing medical billing on the side in addition to my full time job as a practice manager, I literally never had a day off for YEARS. Even when I was on vacation, I had my laptop with me, and was doing the side billing work. Because there was no one else to do it, and it had to be done. I had to choose between staying up until all hours of the night after I got home from my full-time job to get the billings done, or to do them on the weekends. I opted for the weekends, so that I could get good sleep M-F nights. This worked for me, because I don't have kids, and I have a very understanding husband. Each situation is different.
2. Do you know of anyone who is currently doing this?
Yep, me!
3. Are there any conflicts working both as a in-house & freelance medical biller?
For me, there hasn't been any conflicts. All of my side billing jobs have been for companies/practices that are not in the same state as the office I manage, and I would never outsource the billing from my practice. That said, before I took my first side billing job, I did tell the owner of my practice I was doing so, because I wanted her to be in the loop.