Sure, we can discuss about Greeces minority policies or lack of them, but it is hard to belive, that singing in any language would be prohibited, I dont care what "yannis" says (or don`t say).It's not an odd thing at all. See, there are no ethnic minorities in greece (!) The deffinition of being greek there is to speak greek and belong to the greek orthodox church.
Giannis is pronounced yanis in greek. It's not the italian dzhani pronunciation.