WordPress uses a .htaccess file in it's root to provide extra server configuration to the Apache web server to ensure that the application runs smoothly. If you are using the Nginx web server, .htaccess files are ignored, meaning not all functionality of WordPress will be available. Instead, Nginx uses it's own config files to provide the same functionality as a .htaccess file, albeit with different code/syntax.
When WordPress is integrated into Magento, most people assume that you need to add custom code inside the .htaccess or Nginx config file to get things working, however this is false and the default code provided by WordPress will work perfectly. WordPress.org provides the code required to get WordPress and WordPress Multisite working when using Nginx.
Below you can find links to the relevant WordPress.org pages that explain how to setup WordPress and WordPress Multisite for Nginx.
I cannot provide support for configuring WordPress or WordPress Multisite to work with Nginx but the articles above should be enough to get things working for you. You do not need anything custom just because you are integrating WordPress into Magento and the code in the above articles will be enough.