One Database and Credential
Seravo's WordPress service is meant only for WordPress sites. WordPress needs one database and one credential, and those are there for this purpose. We don't offer additional database credentials for the same price or plan or any other arrangements for other applications.
Multiple Sites in One Database
Multisite refers to a WordPress installation that allows you to manage and maintain multiple sites through a single installation, rather than each site having its own, separate site environment on the server. Seravo's service includes support for multisite in the WP Corporate and WP Enterprise service plans.
Use WordPress REST-API Interface for Integrations
We recommend doing integrations between WordPress and other applications by using the WordPress REST-API interface. Making changes to the database or integrating applications directly bypassing WordPress might lead to undesired surprises in the future and considerable additional work for maintenance and development. Therefore we don't recommend it, even if it might seem like a convenient short-term solution.
See also the answer to the question Can I install software other than WordPress on the server?