To answer the titled question, of course! There’s no reason to not engage in a conversation with a self-professed atheist. A Christian will not “catch something” from them as if the atheist has some sort of disease. Conversing with an atheist will not cause you to lose your salvation. You may, however, find your patience to be tested and slight aggravation from their responses. Keep in mind how Jesus responded to the Sadducees and Pharisees. We are to be Christ-like in all things.