The way it reads in Tac Ops ARAD only gives a -1 to-hit when used in conjunction with iNARC.
• ARAD Missiles are more accurate against any unit that actively emits electronic signals, and receive a –1 to-hit modifier and a +1 Cluster Hits Table roll
modifi er if the target is using at least one of the following systems: Active Probes (of any kind), Artemis fi re-control systems, the Blue Shield system,
C3 systems (of any kind), communications equipment (3.5 tons or more), or ECM suites (of any kind). These modifiers are not cumulative, even if the
target unit is using multiple electronic warfare systems. This effect also occurs if the target has been tagged by a friendly Narc or iNarc homing pod.
However, the ARAD missile does not receive any further to-hit bonus from the pod
• Against any target not using the above-listed electronic warfare systems, ARAD Missiles suffer a +2 to-hit modifier and a –2 Cluster Hits Table roll
modifier (to a minimum result of 2).
Reading through the rules, ARAD is a type of munition and as such isn't a NARC munition. The only thing that ARAD is effectively doing is keying in on the fact there is a NARC on the target to fulfill the conditions of -1 to-hit and +1 Cluster.
http://bg.battletech.com/forums/index.php?topic=2723.msg68360#msg68360http://bg.battletech.com/forums/index.php?topic=26824.msg613369#msg613369http://bg.battletech.com/forums/index.php?topic=26886.msg687580#msg687580*edits to provide ruling links