Merge two drupal views with different base types ('user' and 'node') Is it possible to merge two views, one based on users and one on nodes?

The purpose of this is to create a directory of contacts, however some of the listings will be site users and some will not be - they will be created by admins.

It has crossed my mind to just use a content type that users can create; the downside of this is that if they update their details they'd have to update their node too...
Why not simply use a content type only?

You can for example add an optional user reference field to a content type, which points to the user to whom the contact belongs. Then you can embed the content type into the user profile, if you want that. For example by using the Panels project.

For normal users, you could write a few lines of custom code to automatically populate the user reference to the current user and hide the field from them. You could also add a check that they can only create a single contact, if you want that.