Summary:
Even according to ר"א a שטר מתנה that was signed by ערכאות and there were ע"מ ישראל would be פסול (if not for דינא דמלכותא) because of the concern that there may not be ע"מ ישראל and then it is פסול since the ערכאות have no power to effect a קנין.