Vague questions are always red flags in an interview -- there are too many possible ways of answering to be able to determine which is the "right" answer, and applicants will tend to start looking for where the trick is, since it sounds like a trick question.
Not the right applicants. For most positions (except the ones where you're a very small cog in a very large wheel) you have to be able to deal with people too.There was one question in a recent interview that my wife conducted, to which the applicant replied "I can't answer that without knowing more about the requirements." Which was exactly the right answer. He got the job.