Yes, officers CAN process you as a foreigner even at a "Thai nationals" desk. But I've found around the world that, unless you're specifically invited by an officer to come up, lining up in a domestic passport lane is the way to get your head bitten off by staff. It happened to me most recently in Malta, even though it was an innocent mistake (I was tired and bleary-eyed and got into the wrong line unintentionally, and I was still told to get lost).