Probably this would be my biggest dislike as well. When paying for a seminar I am not looking to have a major killer PE warm up workout before the seminar starts. I am looking and paying to learn techniques and different training methodologies. Now if a killer workout happens while learning he techniques that is absolutely great.Just not the brutal warm up workout before hand as that does not really involve any learning experience.
If the instructor (or his reasonable designee) leads some appropriate warmups prior to beginning the material -- I think that's fine. For example, if the seminar is on long stick, and the instructor starts by teaching some stretches & warm up exercises for long stick, or any similar situation where the warm up is geared to specifically preparing for the "meat" of the seminar.
But if they just want to watch the attendees doing jumping jacks and other calisthenics... that's wasting time. If it's a 2 hour seminar -- and the first hour is lining up, doing calisthenics, and other stuff with no relation to the topic of the seminar... that's just being disrespectful of the group's time.