Who nudges the nudgers?

Nobody, because they're rational and unbiased, honest:

It struck me during Chris Wylie’s commentary about the use of “behavioural science” that his language reflected the central ideas of nudge theories, he was using words like “heuristics”, “cognitive bias” and so on. He outlined the basic premise of nudge, too – the idea that humans are fundamentally ‘irrational’. (Yet curiously, those ‘choice architects’ claiming that they know what is best for society and individual citizens are exempt from that theory).

And if you believe that you're welcome to trust them.