If you invited them to your company, then just run a screen recorder, like camtasia on the machines.
If its remote, ask them to record their screen, ie, using camtasia. Since they are testing you should be able to have this a pre-requirement for testing.
Don't complicate things by trying to hide trackers etc for testers, they may be using blockers, doing some weird things etc.. just tell them.
Please record everything while trying to break our app.
That way you will receive 100% tracked material for your review, Instead of worrying about bugs in your tracker app.
If you just using normal end users to test your app... you may as well ask your mom to try it out and watch her do it. Proper testing is a different ball park.
If it were me, I would disable JavaScript - boom, your tracker is down instantly. Disable flash, boom flash tracker down. Try various browsers, mess with dodgy caches, download throttling, behind the scenes POST via Fiddler, any of that can break your tracker, and only then fill in the form like a good boy. Plus you wont be able to see WTF they actually did to break your app! This is the purpose of testing.