Yes! SlickStack uses real, virgin, 100% authentic MySQL — not one of the other database engines like MariaDB, Percona, or otherwise. This is for the very simple reason that Ubuntu LTS still defaults to using MySQL because their (massive) operating system community has determined it is still the “better” choice for a variety of reasons. Since our goal is trusting the upstream stack as much as possible with SlickStack to reduce conflicts and improve stability, we also stick with MySQL.
The amount of staff and enterprise clients involved with MySQL absolutely dwarfs any other database community. While MariaDB has gotten trendier among the open source community in recent years, their team is much, much smaller, and as time goes on they are having a more difficult time keeping up with new performance features that are released in MySQL.
While MariaDB has some cool features that MySQL does not have, nearly all of them do not apply to a LEMP stack server running WordPress.