I don't think we can assume that just because somebody accepts a job working for the President necessarily means they necessarily condone the tone of his campaign or ever judged him to be a good choice for president. They can of course be judged on how they influence and shape policy proposals, and their participation in the process might well be much better or much worse than a principled boycott.

Peter Thiel is not somebody who has simply refused to rule himself out of serving, however. I do think we can judge people for donating large sums of money to the Trump election campaign and subsequently being appointed to a position of power, both because they signalled strong approval of Trump and his campaign with their wallet and because (like major donors appointed to high office in other administrations) they can readily be accused of paying for positions of power.