I have heard that some phrases may be used in a humble form when speaking to a superior regardless of whether or not it has an impact on the superior. でございます is one of them.
But does that only apply when talking about oneself?
For example, 私は学生でございます is valid when speaking to an interviewer. But can I also say 田村さんは学生でございます if 田村さん is my colleague? How about if the person is my brother, i.e. 弟は学生でございます? Similarly, what if I don't know the person?