ECM is a tricky bitch, but the guardian system is 'smart' enough to only screw with sensors and Targeting and Tracking; it can only overlay comms with static, which sufficient transmission power can punch through, but it's not a universal blanket; the user of the ECM tends to choose which channels to jam, so an ECM 'mech can stay in contact with the rest of his or her force while playing merry havoc with the enemy's sensors.