Sigh. Chaps... It's got _nothing_ to do with what you can see and cannot see whilst in the game, and what the fogging distance is. Forget trying to deceive yourselves that this is somehow "not worse than what you'd be able to see in-game any case"...
The server will send positional updates for objects to your client within a certain range or "scope" that is "interesting" to your client. That's how most modern FPS's netcode works. Whether those objects are hidden behind others or within visible range or not, is irrelevant. It is THIS information that is being used to draw the overlays in these screenshots. Not what is "visible" to a human. XYZ coordinates are being intercepted, and "enhanced" via means of these crosses.
What you can see on the screen has got NO relation to what gets sent to your client. The fact is that this thing prolly injects some code into the .exe, and monitors coordinates for any "in-scope" object. Recall Happymod's FlagFinder. The flag didn't have to be in view for it to be able to tell you where it is. Same with T2's HappyMod perma-iff's/object locators.
* TheRoDent puts $10 on a screeny appearing shortly that shows a monstrous overlaid flag indicator, and some snazzy height lines that shows precise spampoints for deployables, inv's etc...