Why sign a contract? Wouldn’t it be easier to hire an employee as a freelancer?
You can hire the Ukrainian citizen as a free-lancer or by contract. The taxation responsibilities are strictly up to the Ukrainian citizen to self declare their employment status. You will not be responsible for making any taxation statements to Ukrainian authorities. It is up to them to declare their income in Ukraine according to the laws of Ukraine. Your expenses can be expensed out according to the laws of the country that you’re hiring from.