I got a conflict of the packages, when 'zabbix-server-mysql' and 'percona-server-56' trying to remove each other during the package upgrade. It was a bit difficult to track down, but the outcome is:

Official zabbix server:

Package: zabbix-server-mysql
Source: zabbix
Version: 1:2.2.2-1+wheezy
Architecture: amd64
Maintainer: Kodai Terashima <[email protected]>
Installed-Size: 7599
Pre-Depends: debconf
Depends: libc6 (>= 2.7), libcurl3-gnutls (>= 7.16.2), libiksemel3, libldap-2.4-2 (>= 2.4.7), libmysqlclient18 (>= 5.5.24+dfsg-1), libodbc1 (>= 2.2.11) | unixodbc (>= 2.2.11), libopenipmi0, libsnmp15 (>= 5.4.3~dfsg), libssh2-1 (>= 1.0), libssl1.0.0 (>= 1.0.0), libxml2 (>= 2.7.4), debconf (>= 0.5) | debconf-2.0, mysql-client | mariadb-client, fping, adduser, dbconfig-common (>= 1.8.19), lsb-base
Recommends: mysql-server (>= 4.0.16-2), snmpd, snmptt
Suggests: zabbix-frontend-php, logrotate
Conflicts: zabbix-proxy-mysql, zabbix-proxy-pgsql, zabbix-proxy-sqlite3, zabbix-server-pgsql

DotDeb zabbix server:

Package: zabbix-server-mysql
Source: zabbix
Version: 1:2.2.2-1~dotdeb.1
Architecture: amd64
Maintainer: Guillaume Plessis <[email protected]>
Installed-Size: 2935
Depends: libc6 (>= 2.7), libcurl3-gnutls (>= 7.16.2), libiksemel3, libldap-2.4-2 (>= 2.4.7), libmysqlclient18 (>= 5.5.24+dfsg-1), libodbc1 (>= 2.2.11) | unixodbc (>= 2.2.11), libopenipmi0, libsnmp15 (>= 5.4.3~dfsg), libssh2-1 (>= 1.0), libxml2 (>= 2.7.4), ucf, fping, adduser, lsb-base
Recommends: mysql-server, snmpd
Suggests: zabbix-frontend-php, logrotate
Conflicts: zabbix-proxy-mysql, zabbix-proxy-pgsql, zabbix-proxy-sqlite3, zabbix-server-pgsql, zabbix-server-sqlite3

Debian zabbix server:

Package: zabbix-server-mysql
Source: zabbix
Version: 1:2.0.9+dfsg-1~bpo70+2
Installed-Size: 2565
Maintainer: Christoph Haas <[email protected]>
Architecture: amd64
Depends: libc6 (>= 2.7), libcurl3-gnutls (>= 7.16.2), libiksemel3, libldap-2.4-2 (>= 2.4.7), libmysqlclient18 (>= 5.5.24+dfsg-1), libodbc1 (>= 2.2.11) | unixodbc (>= 2.2.11), libopenipmi0, libsnmp15 (>= 5.4.3~dfsg), libssh2-1 (>= 1.0), ucf, fping, adduser, lsb-base
Recommends: mysql-server, snmpd
Suggests: zabbix-frontend-php, logrotate
Conflicts: zabbix-proxy-mysql, zabbix-proxy-pgsql, zabbix-proxy-sqlite3, zabbix-server-pgsql, zabbix-server-sqlite3

The notable difference is that official zabbix server package put hard dependency on 'mysql-client | mariadb-client', where other packages merely rely on libmysqlclient18 (>= 5.5.24+dfsg-1) dependency.

That's not a problem by itself, but one of the mySQL-compatible replacements, Percona-server-5.6 provides nysql in the following way:

Package: percona-server-client-5.6
Source: percona-server-5.6
Version: 5.6.16-64.1-563.wheezy
Architecture: amd64
Maintainer: Percona Server Development Team <[email protected]>
Installed-Size: 38104
Depends: debianutils (>= 1.6), libdbi-perl, percona-server-common-5.6 (>= 5.6.16-64.1-563.wheezy), libperconaserverclient18.1 (>= 5.6.16-64.1-563.wheezy), libc6 (>= 2.11), libgcc1 (>= 1:4.1.1), libncurses5 (>= 5.5-5~), libssl1.0.0 (>= 1.0.0), libstdc++6 (>= 4.1.1), libtinfo5, zlib1g (>= 1:1.1.4)
Breaks: mariadb-client, mariadb-client-5.5, mariadb-client-core-5.5, mysql-client-5.0, mysql-client-5.1, mysql-client-5.5, mysql-client-5.6, mysql-client-core-5.1, percona-server-client-5.1, percona-server-client-5.5, percona-xtradb-client-5.0
Replaces: mariadb-client, mariadb-client-5.5, mariadb-client-core-5.5, mysql-client-5.0, mysql-client-5.1, mysql-client-5.5, mysql-client-5.6, mysql-client-core-5.1, percona-server-client-5.1, percona-server-client-5.5, percona-xtradb-client-5.0
Provides: virtual-mysql-client

Seems, both variants are used now in Debian packages, so, for example, Redmine requires:

Depends: libmysql-ruby, mysql-client | virtual-mysql-client

Can you, please, do the same, and require:

Depends: mysql-client | virtual-mysql-client | mariadb-client