RPM in mariadb repos is called 'MariaDB-server'.

mysql/server.sls

@@ -105,7 +105,7 @@ mysqld-packages:
     - require_in:
       - file: mysql_config
 
-{% if os_family in ['RedHat', 'Suse'] and mysql.version is defined and mysql.version >= 5.7 and mysql.serverpkg != 'mariadb-server' %}
+{% if os_family in ['RedHat', 'Suse'] and mysql.version is defined and mysql.version >= 5.7 and mysql.serverpkg.lower() != 'mariadb-server' %}
 # Initialize mysql database with --initialize-insecure option before starting service so we don't get locked out.
 mysql_initialize:
   cmd.run:
@@ -116,7 +116,7 @@ mysql_initialize:
       - pkg: {{ mysql.serverpkg }}
 {% endif %}
 
-{% if os_family in ['RedHat', 'Suse'] and mysql.serverpkg == 'mariadb-server' %}
+{% if os_family in ['RedHat', 'Suse'] and mysql.serverpkg.lower() == 'mariadb-server' %}
 # For MariaDB it's enough to only create the datadir
 mysql_initialize:
   file.directory:
@@ -144,9 +144,9 @@ mysqld:
     - enable: True
     - require:
       - pkg: {{ mysql.serverpkg }}
-{% if (os_family in ['RedHat', 'Suse'] and mysql.version is defined and mysql.version >= 5.7 and mysql.serverpkg != 'mariadb-server') or (os_family in ['Gentoo']) %}
+{% if (os_family in ['RedHat', 'Suse'] and mysql.version is defined and mysql.version >= 5.7 and mysql.serverpkg.lower() != 'mariadb-server') or (os_family in ['Gentoo']) %}
       - cmd: mysql_initialize
-{% elif os_family in ['RedHat', 'Suse'] and mysql.serverpkg == 'mariadb-server' %}
+{% elif os_family in ['RedHat', 'Suse'] and mysql.serverpkg.lower() == 'mariadb-server' %}
       - file: {{ mysql_datadir }}
 {% endif %}
     - watch: