My inner singer is a dangerous character, and is best left very closely guarded!!!
I dont think so. Art teachers in general dont necessarily have to be successful ( if that means they sold many of their works) in order to be great at instructing others of his/her processes. They must be good communicators, have a passion for what they do and have a plan for their students.
This is an interesting topic, but you need to define what an artistic 'all-rounder' is... It could be a person that has a wide and varied view and notion about arts, which to me translates to art theorists. Otherwise I haven't understood your question well and I am sorry about that. I teach photography in FE and I think there is space for both successful practitioners and art theorists in educating aspiring photographers. I think there should be variety of tutors, who are experts in different disciplines within the subjects taught, in any educational institution so there can be balance in the learning environment.
The risk with only having art theorists in a course is that there can be minimal links with industry and not enough practical guidance on how to survive life after college. As a student, you might get a varied knowledge on a subject and wide exposure to work by interesting artists, which is definitely inspiring but you might not acquire skills that are immediately usable in the market and you will probably need to spend equal amount of time doing that after college.
The disadvantages of having tutors that are experts on one area or another within a discipline means that students could miss out on skills that are not covered by the knowledge-base of the tutors.
This is my take on your question, if I got it wrong, could you please explain what you mean by artistic all rounder and what level of education you are referring to?