Personally, I wouldn't hesitate to use a database if it's a supported configuration by the vendor (aka 'upstream') with binaries they provide. Adding a repo (or equivelent) isn't a big deal because I am going to have to have some way to manage configurations anyways.
It's more important to me for upstream support then distro support... but whether or not I choose to do that depends on the circumstances.
Usually I am not concerned with the database so much because when I, and most people use databases, it is generally because we have a app or framework we want to run that depends on them. The configuration and everything is going to be managed by the application install scripts and deviating from their documentation just means irritation and time spent on something that isn't really going to matter.
If the MariaDB folks want to have people use their software then the biggest first step is going to get the distros to swap in their software in replace of Oracle's. This sort of thing happens fairly frequently with software in distribution repo's.