I think this quite a common situation, there should not be any problems if you play your cards well. My question is, why is the half in CH registered as single? I am not sure if it depends on the canton but he should actually pay less taxes if he was registered as married. It should not matter where the other half lives. Anyway, like mentioned before, everyhing is registered and they will propably find out that you were married if you both end up in Switzerland. Not sure if it such a big crime after all, especially if he's paid more taxes than he should.

Any tax specialists out there?