No point him buying the 3g version, unless he knows he won't be able to log on to a data network provider in Poland. It works differently to a phone. He'll need a data package in Poland.
He could use the wifi, but he'll need a Polish carrier that has the micro sim and a data package for the iPad for which there is none as it is not officially available in Poland. If he bought and registered a data package in the US then when he returns to Poland he will pay roaming costs.
I say just buy a wifi, or alternatively the 3g version but knowing he couldn;t use it in Poland (for the time being).