How can I import a local database remotely without having a local database copy?
Well, there are two things that can be done with this.

1) Database sanitisation

You can write custom Drush sql-sanitize scripts that will sanitize the database, for example changing all usernames and passwords, as well as any other custom alterations required. 

Drush SQL Sanitize scripts can be set up as webhooks, to ensure the sanitization happens automatically.

2) With D8, you mostly shouldn't need to give anyone the database at all. Functionality is migrated through configuration and the configuration API. Developers can work on code, then export their configuration, and push both the code changes as well as the exported configuration to the remote server. The configuration is then imported into the remote environment's active configuration in the database, providing the new functionality on the remote server. 

I wrote a blog series on the Configuration API to help understand it better: https://www.morpht.com/blog/drupal-8-configuration-part-1-configuration-api