Ken McGrew wrote:
If Sensei doesn't call them on it, it will continue.
I agree Ken, everything that happens in the dojo is the Sensei's resposibility. if there is 'bad' ukemi going on, then it is the Sensei who allows it.
Of course, that doesn't mean that 'bad' ukemi shouldn't/doesn't take place. The teacher should be close enough to all their students to know ( by taking ukemi themselves perhaps
) what each student is like. Each student should be crystal clear on what the teacher wants them to aim for when they practice the role of uke. This may be different for the different 'styles' of aikido, however, if there is confusion, the teacher needs to take responsibility.