Unless the Israelis were jamming heavily (and thus impeding reception of IFF signals), and had their jamming aircraft sitting where the Russian plane was between them and the Syrian missiles in case the Syrians launched in "home on jam" mode.
ECM aircraft have more than one e-weapon at their disposal than a high power, static-noise jam. They can also fool the receiving radar into thinking that there are more or fewer aircraft and spoof them miles away from their actual position.