Do interviews require taking vacation days?
You should ask your advisor, but it is reasonable for an advisor to allow you time (potentially several weeks or months) to essentially be away from the lab and your research in order to interview for jobs. In my opinion, this is a concession that is reasonable to give as a reward for hard work during previous phases of an advisee's research. If not, the advisor likely does not have the advisee's interests in mind. That could come back to bite him/her later when attempting to find new advisees.

On the other hand, if you're spending a lot of extra leisure time on the trips that is not part of the interview, then it should probably be considered vacation time.