To some extent, I think you may be asking the wrong question. The students you are talking about grown up adults, fully capable of making choices and understanding the consequences. I wonder if your actual question is something like:
What are effective ways to deal with misuse of mobile devices in class?
You'll notice there are quite a few answers on this question, which may solve you real practical problem, yet none of them involve monitoring the students’ devices or anything else. I suggest that you address your problem directly:
- tell the students your expectations,
- set up rules that will govern the use of electronic devices,
- enforce the rules when you are aware of a violation.
Frankly, the fact that a student would be using an iPad for purposes other than you had planned, if it doesn't prevent him or the others from learning, is not a bad thing. You can't think of everything, and surely some of the students will come up with creative yet constructive ways to use the device.