I think that a survey of professional programs will produce very mixed results about how many faculty have a substantial period of private or public practice prior to becoming faculty. In particular, I question whether many faculty had significant decisions in possitions with significant responsibility in private practice.
Law schools are the same, many are part time faculty with full time law practices.
I think that most tenure track LA faculty have relatively little significant experience prior to becoming faculty. I think that LA progams benefit from such faculty, even without experience in office practice. I think that this is changing. I think that a common set of evaluation standards for promotion and tenure among all faculty on a campus is in our future. It will be based on scholarly productivity and value added student evaluations.