Is there any way to hide page from dashboard (all pages list) OR navbar from plugin function?

I do not completely understand what you are doing, but I get the feeling that you have greatly over-complicate this. You don’t have to create a “Page” at all to load a custom template. You can hook to template_include and simply include a plugin file with much less effort than you are currently going through.

For example (stolen form another answer):

add_filter( 'template_include', 'portfolio_newpage_template', 99 );
function portfolio_newpage_template( $template ) {  
  get_header();
  include('/some/file/path/file.php');
  get_footer();
  die;
}

Honestly, I think that is all you need to do.

However, if you need parts of the page to be editable you can register a post type such that it does not show up in the menus but is still accessible if you know the correct URL. These two arguments to register_post_type will do it:

'show_ui'            => true,
'show_in_menu'       => false,

You will need to create some kind of interface for associating the posts with your users (I think) and for accessing the edit screens.