Does Valve use color correction entities for their destroyed maps? If so, what sorts of settings do they use.

There are only four RAW files in \materials\correction\, which would lead me to believe CC isn't used as extensively in Portal 2 as it was in Portal. That being said I haven't checked many of the stock maps, so I can't accurately say.

Also, none of those four RAW files are labeled destroyed or similar.

However if you take a close look at the global_ents instance... (as far as i know) every relay/setting enables a certain colour correction. I've been using whichever looks best in my destroyed chambers... don't care if it was actually intended for clean chambers

Which ones do you recommend?

Like i said...just choose whichever one looks best... well if you intend of keeping your own fog settings then its difficult... i'd say just mess around with the global_ents a bit... try different ones.. and if you find one that suits you, you can copy/paste and alter the fog settings more to your liking.