It might be beneficial for all the nursing staff to have a round table discussion regarding evaluations. Perhaps co-workers can help identify any deficits or suggest strategies to overcome the negativity. I doubt the other instructors are complaint-free. Have you watched "Restaurant:Impossible" on the food channel? They tape people working in restaurants then interview them later about any negative language or behaviors. It amazes me how the workers deny they did anything wrong, even though the viewer sees it happening live. Could be the students are the same way. If you ask someone to vent, expect them to vent.