Like mimelim said, if it's really important to why you went in to medicine, then I suppose so. Otherwise, no reason to do so. It's not the same as following a religion.
Religious groups are more because of what they do (non-profits, beliefs and principles that shaped you, food drives, etc.). How do you bring up that you're an atheist? It's similar to just being secular, and doing activities that help people, WITHOUT tying in religion.
Sort of like volunteering at a food pantry that is not affiliated with any particular religious denomination. You don't write down that you're an atheist doing it. You just say that you volunteered there. It's different to say "My youth group and I...".
Honestly, I don't know any atheists (aside from Dawkins, etc.) that really discuss how important it is to them. In religion, you feel a strong love for whatever it is you believe.
Atheism, you lack that "entity" or principle to really love and talk about. You're just sort of...whatever. NOT saying the same VALUES aren't there. It's just that, religious groups tie the help and service into their beliefs and teachings of their specific religion. As an atheist, aside from lack of belief, you don't really have beliefs and values or principles that define your atheism.
This, coming from an atheist (more agnostic, I suppose).
To answer your questions, I certainly depends on where you're interviewing. Loma Linda will be more open towards that religious inclination than others, and they have their own "line" in regards to what they consider a zealous individual. But, in general, zealots are not, by any means, favored. It's better to not unnecessarily shake branches. For the most part, people in this profession are very open (you sort of have to be), and you'll be fine. But don't defend or bring up strong beliefs and opinions where it is not relevant.