It is true, ECM is a bright beacon for missile to homing on.
But solo HOJ is NOT enough for SARH missile to hit a target, the missile can only follow the ECM to a very close location(50-100m) of target, terminal illuminating guidance is still required(but the illumination time can be greatly reduced, just illuminating 10sec before impact could also score a hit, as long as U can tell when the missile will impact).