I think PPM meant the Gardevoir Psy-Shadow card, not the Ex one. But I don't know about it, I even play the DR Buffer Piece and DR Energy Recycle System.
Indeed you can. There is no difference between both the Gardevoirs in one way or another (except Art and set symbol) and that allows you to use the older version. This goes the same for Slaking, Blaziken and other reprinted cards.