What evidence do we have they any nominee will act in a particular way once they have been appointed? None, none whatsoever. Once on the Supreme court they answer to no one and can do as they please.
The best guarantee you can have that this will not happen is if you have personally know the candidate for a long period of time. President Bush knows Harriet Miers much better than any other candidate, hence the reason for picking her.
I'm sure George Bush and Miers have had lengthy talks about Constitutional philosophy. Bush isn't a lawyer and has not demonstrated that he knows the first thing about Constitutional law himself.