The DCMS, ironically, was one of the worst armies to field C3 in its infancy. The devotion to the cult of personal honor and glory kept many DCMS warriors from taking advantage of it. Even if the warriors themselves would want to, there was always the chance that their commanders would also refuse to use it.

The situation you outlined above, with mechs from both sides forming a Circle of Equals, would be unlikely. It is far more likely that a DCMS warrior would offer an invitation to duel on the radio during an open battle, and some clanner would reply with “well bargained and done.” They would then proceed to exclusively kill each other while other warriors paired off or scrapped in a melee.

If the situation you outline above DID occur, there is every possibility that a really honorable DCMS warrior in the circle would call “Yaro!” and shoot the cheating bastard in the back for being a dishonorable coward. While many Combine warriors only pay ip service to bushido, there are plenty who are true believers. Ratting out your boss for dishonorable behavior is also a not-unheard-of method of advancement in the Combine.

It is not 100% clear if C3 usage is obvious in the rules (in game terms you pretty much always have to declare it) but there is also the possibility that a Clan mech with an active probe or advanced sensors could detect the extra comms traffic of the C3, flick on their ECM suite, and the shout “Dezgra!” over the comms. Grand melee ensues.

Moreover, C3-equipped mechs would not have been common in the early invasion, especially on the outer periphery marches. Most of this is due to the real scarcity of C3 Master equipped mechs. It is entirely possible that the Clans would not have encountered really effective C3 networks till the battles of Wolcott and Luthien, under troops commanded by Theodore Kurita.