[WillPostForFood]

Here is an article with a tour of the GM teardown facility, so automakers unquestionably do it.

http://www.slashgear.com/the-auto-vivisectionist-inside-gms-...

That said, there is pretty much no US market for diesel outside the European imports. So they may not be focused on their diesel competitors enough to have done the teardown/research/testing to discover VW cheating. I find that more plausible than everyone cheats and everyone knows everyone else cheats.