I had always assumed sacred harness was necessary to proc hammer jammers via the free judgment when using falling sword - unless you had a separate blind/stun/immobilize.
While experimenting with a Seeker-6 Captain Crimson-3 build, I dropped sacred harness and tested falling sword runes. Interestingly enough, all runes for falling sword were yielding a 5x damage boost on mobs hit by falling sword. My best guess is that falling sword itself has a brief immobilize mechanic. All runes also proc strongarm bracers.
While it doesn’t hold a candle (Seeker set pun intended) to Aegis of Valor, a Hammerdin build with CC3 and strongarms is doing more damage than the traditional CoE version while having more toughness (through Laws of Valor - Unstoppable Froce) than the unity version. The only loss seems to be that falling sword has a smaller area in which it procs hammer jammers relative to judgment.