hmm.... Well for now maybe we'll just document that it has to be a unique user for this service. That's generally a standard good practice.  However, it does mean multiple services that are supposed to have the same user won't quite work. In that case, you want a DEB which adds the user/group, and then depend on that I think.  In that case, you're probably directly implementing things.

SO, I'd say how it is now is fine for now.