Not trying to be mean, but your arguement is somewhat invalid. Here's why:
A. The agreement you mention is not about releasing maps with custom content. It's about selling your maps you make which is illegal.
I suppose it doesn't matter if you make a map with them or not, just that you associated them with the "New Game Materials". Either way it violates your contract.
B. I release maps with custom content, yet they are legal. Why? I own the game I port models from, and release the maps for free. Perfectly legal (according to the Activison agreement).
This is a really good argument that people like to use this to justify ripping assets from games, but the matter of the fact is that your ripping assets that you didn't have explicit permission to do so, and as the contract puts it:
New Game Materials must not contain any illegal, obscene or defamatory materials, materials that infringe rights of privacy and publicity of third parties or (without appropriate irrevocable licenses granted specifically for that purpose) any trademarks, copyright-protected works or other properties of third parties.
So yes, you are violating the agreement to a degree if you rip assets from Black Ops 2 or Ghosts.
C. It's illegal if I give assets to another mapper who doesn't own the game. That's stealing and illegal.
This is what i meant by "Illegal", i should have been more specific. But yeah, a lot of users within the community like getting their friends to port them assets that they haven't legally purchased themselves.
D. Technically, the UGX Mod is then illegal (if you don't own black ops or other games assets are from). Not hating in UGX here, it's a great mod.
Because the UGX team has legally bought copies of Modern Warfare and Black Ops, they have the right to add them to World at War as a "mod" (as allowed by the written agreement that comes with all mod tools), even if the files in the "mod" contain assets that a user who doesn't have them plays the "mod" its still covered by the agreement.
However, i can not say the same for the weapons from Modern Warfare 2, Modern Warfare 3, and Black Ops 2 that are in the mod.