Would repeating a course in which I received a U be considered as a second attempt?

Yes. U grades mean that you did not earn credit for the course. If it is a required or core course in your plan of study, it would have to be repeated. If it is an elective course, then you could choose to repeat the elective course or you could pick a different elective from those allowed as part of the degree. You would still need to meet the necessary elective credit hour requirement for your degree plan of study.