Can two nodes have same URL using Pathauto? I know that Drupal allows same url for multiple nodes.
But I've a scenario: a registered user creates and submits an article as an unpublished node and assigned an URL by pathauto based on its title. 
At the same time another user creates an article with same title in unpublished form. Will it too have same url?

I'll not "publish" those nodes anytime. I'll (as an admin) simply create a new node and copy paste contents.
a registered user creates and submits an article as an unpublished node and assigned an URL by pathauto based on its title. At the same time another user creates an article with same title in unpublished form. Will it too have same url?


No. pathauto by default will append a number to the end of the URL to differentiate between them.