"Know that they can code" and "know how they code" are different things, and it's possible the latter could effect how well they fit into your team. Whether an interviewer can actually do a good job assessing that is another question...
Excellent point. Those are definitely two different things and are both important, but I would argue that you can determine the "how they code" component during the interview as questions about previous projects, rather than making them write code in front of you. And again, a short-term contract would also work to solve this goal while not wasting my time.
"How they code" can be slightly answered by looking at the commit history of their code samples (Which they have on github / bitbucket / other site... right?)
Not really. I'm talking process more than result. The question is whether their process and your processes mesh well, and watching them work on something could well provide information that static commit histories lack.
As mentioned, I'm a bit skeptical that an interviewer can reliably extract that information.
