mote24, I am not sure exactly what you are asking.
If you are asking if working as a waiter can be used as proof of the at least 20 hours employment required to maintain your OPT, the answer is No. You are required to be doing something that's related to your field of studies. But the interesting thing is that the only thing you have to report is the company's name and start/end date. So, how will they find out what your job title is? I have no clue. I don't think they try to find out.
If you are asking if working as a waiter while on OPT is legal, the answer is again No. OPT allows you to legally work in your field of studies, that's it. It doesn't allow you to just work anywhere, doing anything you want. But then again, everyone does it and people rarely get in trouble for it.
Hope that helped.
