It works with all the major terrain elements, so it should be ok? There are some things you have to bear in mind though, also check out the command depot for more info on the KnowsAbouts command.
If you move close enough to an AI (20-30 m depending on its skill) the KnowsAbout will automaticly goto 4, regardless of wether the AI can see you or not. Try putting a west guy directly behind a russian in the editor, as soon as you move he turns on you.
Not sure, but this means it's impossible to sneak up to an AI soldier?
The KnowsAbout level will slowly fall to a lower value when the AI loses sight on a target, so if you hide the AI will slowly forget about you. It will goto higher values instantly.
Beacues it takes time for the value to reduce, it can appear as though the AI can see you through bushes and such.
Forest objects reduce LOS but do not block it, so if you want to stay out of sight of AI, move around the edge of a large forests.
Like I said the it depends on the scenario\terrain e.t.c Best bet is to monitor the value during your mission and see if you can use it to do what you want.