To what extent should UML be covered in the context of a degree?
From my software engineering experience.

Some of it is useful some is not. It was put together by a committee of organisations that had a product to sell. (state machines got in there because a committee member had a state-machine editor.) A lot of other useful stuff was missed out. 

Take what is useful, leave the rest, and use stuff from elsewhere. 

There is nothing unified about it. I have used mainly class diagrams, some dataflow (I think it may be called), but as you say not too much formality. We never passed them through a linter. At one time we were drawn in to using them to create code. This was an expensive lesson.

Most of the diagrams (may be all) existed before the UML. I tell my pupils that some of the diagrams are useful, but also look else where. I tell them which ones I have found useful. And I tell them what I have said here: there is nothing special about the UML (or the process of collecting together, arbitrarily, some diagrams notations).