How to show Users and Nodes in a single view?
One option is to add a user view as a footer to the node view. The footer can be configured to inherit the same contextual filters as the main view.

You can't get joint paging or joint filtering using this approach but it works in some scenarios. 

I've also hacked into the views hooks before and manually created a db join but that is a nightmare to maintain so I wouldn't recommend it.