I think shunned is a very strong word. I am allergic to alcohol ao I can't drink but I don't feel pressure to drink. Once they know it is for health reasons, I think that people are usually quite accomodating. On the other hand, drinking (especially with co-workers) together is a popular and cherished past-time of Koreans - so they may feel a little bit awkward in this situation. If you make them feel at ease, then there should be no problems.