When installing a new Wordpress site, Ploi asks for the database to be used. This option is only available if that server also has a database server installed.

I am however experimenting with setting up separate app and database servers. My suggestion is for Ploi to allow, when installing a new Wordpress site, selecting a different database server if one is available, and/or allow manual credential input, eg., an option called "External database" and then Ploi asks me for the credentials.