Integrating iATS forms through CiviCRM (Drupal) onto website Wordpress
You can embed the Drupal site's form (any form, whether from Civi or Drupal) into your wordpress site using an iframe.

Here's an example of exactly that:
https://patientscanada.ca/donate/

There are three steps to make this work:


Create an alternative theme on the Drupal site that is suitable for embedding in an iframe. There's a Drupal theme here: https://www.drupal.org/project/entity_iframe_theme that will take you most of the way. I can share what I've used if you want.
Use theme_key or similar module to display the appropriate path using that theme.
Configure your settings.php to allow the wp site to iframe your drupal pages (by default, Drupal will not allow itself to be used in an iframe, as a security precaution).