Newhart was nominated for an Emmy for a serious role he played on ER. I didn't see it, but I do have trouble visualizing him doing straight drama. However, since his scenes are with Ducky, I don't imagine they'll be all that straight.
Another actor who was a victim of type casting that I always thought could do dramatic roles was Don Adams. I didn't watch Get Smart much; it didn't seem all that funny to me. But in a couple of interviews I saw, Adams was composed, articulate, and quietly authoritative. One time he mentioned that for all the post-series roles he was offered, the producers wanted the Maxwell Smart voice. He never really got away from the role.