To write exams with ChromEx on iPad you need to find your own solution to lock down the devices to protect against cheating. We do not offer any existing solutions at this time but we are working on it.
Software that can lock down ChromEx for iPad
Safe Exam Browser
Safe Exam Browser for iPad works with ChromEx and can securely lock down your students devices and protect against cheating. The teacher have to create their own Safe Exam Browser configuration file for their exam and make sure all their students are using the Safe Exam Browser.