If you build out your D8 site locally in your dev environment using Composer, you'll have Drush 9. Then, if you commit your D8 instance (Git) and pull onto your server, you'll have Drush- albeit you'll have to execute using the full path. For example: From my command line on a Ubuntu 18.04, I can execute
$ vendor/bin/drush pml --no-core
My D8 instance on the Production servers contains the following at the root.
Notice that /vendor is committed and present in this repository. And that contains /vendor/bin/drush
Refer to the Drush Documentation for more info.
Hope this helps!