If I am understanding the questions correctly, if provider is in network with medicare but not with medicaid, you can charge the medicare copays, deductibles, etc to the patient. Once the provider is in network with medicaid, you cannot bill patient at all.
Keep in mind, that all states vary with laws.
At the top of the page of the link I previously provided, click on "Federal Policy Guidance" at top of page, then under "Frequently asked questions" click on "For more information about the increased FMAP rates available beginning in 2014 and beyond, click here." Then on left side of page click "cost sharing". From there you should be able to find more specifics. Hope this helps