Add a views exposed filter block into my theme using template.php
You're actually having an error if you check the php logs:

PHP Fatal error:  Call to a member function get_exposed_input() on a non-object in   
.../sites/all/modules/views/views.module on line 1950


You can't just call drupal_get_form('views_exposed_form') because drupal wouldn't know which exposed form you want to render. Remember that a view or view display have its own exposed form.

If you check where the error is, you'll see that it's caused by not having a view object in the form_state variable.

What I suggest you do is use the Admin Block UI (/admin/structure/block) and just restrict which node types where you want to display the exposed filter.