Assuming pretty permalinks are enabled in settings, WordPress does attempt to add set of rules to the .htaccess.
In a nutshell their logic is to route anything that isn’t existing file/directory to WP’s index.php. After that WP is loaded and tries to interpret URL via its rewrite configuration and other data.
This does not exclude 404s either, they are too routed to WordPress and handled by it, typically producing output via corresponding template from active theme.