Since the labor law has been changed effective 01st Jan 2016, when you make an offer of employment you'll have to be very careful of what you are stating. I do not want to mention confirm date for joining for a new employee so can I mention below as joining date in his/her offer letter :
"Your expected employment start date will be confirmed after the company successfully secures your U.A.E employment visa, provided you pass the required government medical test"
Please correct me if I'm wrong