I don't see any harm in doing so. My biggest concern is educating the community that not every question needs to be migrated, and although Super User moderators are known for having a very strict closing policy, some questions have their merits on Super User rather then AskUbuntu.
However I do think the close reason would be useful.
There is an expanded discussion of what I meant with this in the comments. It might add more value then my actual answer does.