Renaming a theme so it aids SEO and the theme used is hidden

You’ll be unable to automatically update the parent Divi theme when it’s directory becomes renamed.

You can use any of caching​ plugins with CSS minify or/and CSS combine turned ON. This way everybody will see /cache directory instead of the actual theme directory.

Or as the alternative, you can update renamed parent theme manually, directory by directory, file by file.

BTW, there is no any connection between SEO and the theme name.