Sorry, JD, I didn't see your post on the MCAT site or I'd have replied. It depends on the instructor, as many people have already said. Generally Kaplan MCAT instructors are expected to have scored at least an 11 for any subject they teach. Most instructors do specialize (physical science, biological science, or verbal/writing) as at TPR. Some do teach the entire course from start to finish, which is what I do. Sometimes I also sub for the other classes if there isn't another instructor available.
Most students don't seem to have a strong preference one way or the other concerning having a single teacher versus several. Some students even seem to prefer having the specialists since those instructors become "experts" in their subjects. Other students prefer having the same instructor for the entire course; if you are one of them, then you should ask your local center about whether there are any classes taught by a single instructor. You can also ask to meet with the instructor or ask your friends who have taken the course previously who their favorite instructors are.
Either way, remember that the students who get the most out of the Kaplan course are the ones that work hard and complete all of the assignments. The instructor is there as an aid to your studies, but s/he can't do the work for you!