The Clans appreciate winning. If you cheat, and I should have seen it coming, then I've got to nod my head and give you credit. A true warrior has cunning, and tries to win with what he's got against superior forces. Of course, at a certain point, they get pissed off. If you keep cheating, then obviously the rules mean nothing to you and it's time for massed fire.
I think you've got to separate behavior that the Clans would not engage in from truly dishonorable conduct that they hate. For instance, you don't get any honor from an artillery kill. When you're basically fighting for breeding rights, to pass on your genetics, getting stuck in a Naga shooting Arrow IVs at distant targets really sucks. Nobody wants to do that. Nobody wants to pilot the Naga and nobody wants to spot for the Naga. It's a punishment assignment. Now, for Star Colonel Dave, using artillery to wipe out a company of tanks that are over that ridge would be fine. There's no real opportunity for honor in smashing vehicles, so you might as well just bombard them. And if an Inner Sphere mech company is dumb enough to leave themselves wide open to artillery bombardment, well it sucks to be them. You can always play it up that you are full of wisdom and not blinded by raw ambition ("and I'm really humble too..."). But for the warriors piloting the mechs, well they hate it. Therefore the Clans don't use artillery all that much, even when it would make sense to do so.
I think that's probably why they don't use C3 networks. While it's an advantage overall for your side, it's basically like asking for help. You are making it easier for your buddy way over there to assist you in killing your target. Most Clan warriors wouldn't use C3 because they don't want to. There's nothing necessarily dishonorable about it (as in it's not treacherous), but it sure makes you look like a wussy. You might as well say "I'm gonna call my dad!" I don't think it's the kind of thing that would make Clan warriors immediately froth in rage if they Inner Sphere used it against them.
That said, I also don't think the example given, of a Celestial pilot walking his machine up next to a duel between two other mechs, is a particularly good one. I think the average hyper-cocky Clan warrior would simply say "Fine, I'll kill you both!" and unload on the guy dumb enough to make himself an easy target. He's not going to interfere in somebody else's duel, but if an enemy mech is clearly not engaging the guy he's supposed to be fighting, and instead comes wandering over to you? Fair game, man.