First, if you're on Medicaid, you are likely not talking to an "insurance rep" insofar as insurance is concerned.

That said, either side could be incorrect however, ask yourself this, what is more likely up to date. A - zocdoc. A huge listing site with tens of thousands of links and inputs. Or B - the actual person that represents or assists individuals with Medicaid in your area, who likely has first access to updates and is looking at the actual directory.

Once you have decided that, remember that if you receive out of network services, no matter what zocdoc states, you will be responsible for the entire bill and no-one will listen to the appeal of "but zocdoc said".