Only if NSA knows if they are. But what if they don't know yet? Don't you want them to know rather sooner than later? You could easily achieve that by spying on your citizens rather than on the rest of the humanity your citizens might be spying for.
The premise of the preceding question is that the US somehow goes easy on its own citizens when they do things that might justify electronic surveillance. But that's obviously not true; there's just a different process for it.