I will have finished all my classes by the end of Dec. 2016, but according to the McMaster website, convocation doesn't take place until May 2017. Am I still a student until that time, or will I receive my degree before hand? Really, my concern is if an employer needs some sorta proof that I've graduated, will I have to wait until May to provide this? (that really can't be the case right...)

I'm pretty sure when I asked the same question, I was told by the office that you will just pick up your degree without a ceremony. That's the only difference.

You have not officially graduated until convocation, whether you attend or not. You can either get a special letter saying you have completed all requirements to graduate, or apply for special consideration to have your degree conferred early, depending what your employer requires. It's explained on the registrar's website.