What are your reasons for doing this away rotation? (You don't have to answer here, but it's important to know your reasons.)
While the vast majority of people do away rotations in their chosen field in hopes of a successful "audition" and/or to check out residency programs, I'm sure there are other valid reasons to do any kind of away rotation. Doing an away rotation in a different field is unusual, but there is nothing wrong with that, as long as you have a decent reason for doing that and can explain your choice of this (current or future) elective to a random curious residency interviewer.
Another issue is, how seriously are you taking this rotation? I don't think it's a good idea to approach it as an easy rotation and expect to ask for a lot of time off for interviews - it's not only that this is questionable in terms of values/ethics, but worse case scenario you may piss off people at that rotation enough for them to talk to people in your specialty at that hospital (resident to resident, I would expect, remember that social circles are not limited to one specialty/department), which may affect the fate of your residency application at that hospital. So basically, even if it's not a rotation in your specialty, take it seriously and nobody will consider you doing it "super rude".