Ra'ad is used for D-EAD Ops, not exactly S-EAD Ops. ARM are primarily used for SEAD Ops, not DEAD Ops. If ARM serves its purpose to destroy radars, then Ra'ad might not be required to destroy SAM launchers.
Theoretically maybe, practically its yet to be seen.
S-400 can also work on principles of ABM/ACM shield, to stop incoming BM/CM instead of just acting as a basic SAM.
As for the range, it will be a n EW/ECM tug of war. The further a target stays away from the radar (S-400 Radar), the difficult it is for the radar to track and lock it. The close the target moves to the Radar, it becomes easier for the radar to track,lock and fire on it. Similarly, its difficult to jam the S-400 Radar as the EW aircraft gets closer to it, since the transmitter power of S-400 radar would be higher than that of the EW aircraft jammer.
If PAF's AWACS, MPAs and Air-Refueller are with in Pakistan's airspace and protected by EW/ECM of AWACS or DA-20, as they will be receiving radar radiation of the S-400 radar and countering them through their own means and thwarting a lock onto PAF aircrafts, then PAF aircrafts are safe within own air space. F-16 have EW pods that can break locks.