You’ll need to choose a Custom Install to install your own plugins/themes at Dreamhost. The main downside of a custom install is that you’ll also need to monitor WordPress and your plugins for security updates and apply them yourself.
The one-click install page for WordPress at Dreamhost reports:
“What is the Difference between install types?
Simple Install – We install the program, perform all updates. You will not have access to the application files but we have included some themes and plugins. Customization is very limited
Custom Install – You select where to install the app, specify database name, user account, etc. You will have full access to the application files and database”
