I found another article by Robert Quinn on Med Mal experience rating which suggests that as of 1998 it was not common. He states
Unlike many types of insurance, such as automobile insurance, medical malpractice insurance is generally not experience rated, but rather adheres to a type of community rating. For the most part, insurance companies set malpractice premiums according to a physicians’ specialty, type of practice, and geographical location. Although many insurance companies have experimented with experience rating at times, community rating continues to predominate (Sloan 1988). Studies on the subject suggest that some type of experience rating would be preferable for both insurers and physicians (Rolph 1981; Sloan 1988; Ellis, Gallup, and McGuire 1990). The study by Ellis, Gallup, and McGuire (1990) did, however, suggest that, while experience rating moves premiums toward fair rates on average, the average risk adverse physician that physicians in skewed specialties (specialties where a "few bad apples" account for a high percentage of the claims) would have the most to gain, and thus be the more likely to want experience rating.
I also put a question to the ActuarialOutpost discussion list asking if people had experience with med mal underwriting. As of today, I have not received one definitive response that says "Yes, we experiecne rate". So, it is still likely that some firms might do it but it may not be a universal practice.