You can use entity view in your view block instead of the fields. Then in the hook_node_view you will have easy acces to the nid. Or you can use the fields and add the fiels "Nid" and via the views-view-field.tpl.php ou have direct access to the nid.
Full Answer
When you first install a Drupal 7 site with a base theme, you’ll get a couple of standard templates such as html.tpl.php, node.tpl.php and page.tpl.php. But often you are going to need to create a node template for a specific content type.
When creating a template like this, you aren’t actually guaranteed that Drupal will use the template. There could be more than one node template in a Drupal site, so Drupal has to decide which one to use. Drupal will order the template files in the following order: