Note that the steps in the article only allow creation of non-xa datasources with mysql.
If you need xa-datasources, you need to have something like this in your module.xml (note the dependency to transaction api):
<module xmlns="urn:jboss:module:1.0" name="com.mysql">
<resources>
<resource-root path="mysql-connector-java-5.1.22-bin.jar"/>
</resources>
<dependencies>
<module name="javax.api"/>
<module name="javax.transaction.api" />
</dependencies>
</module>
As explained in this irc log: http://echelog.com/logs/browse/jboss-as7/1327618800
Note also that at the time of this writing (14.12.2012) current mysql connector (5.1.22) already contains the file mentioned for type 4 drivers, java.sql.Driver.
Here's a working configuration that defines a non-xa and an xa datasource for mysql:
<datasource jndi-name="java:jboss/datasources/MySqlDS" pool-name="MySqlDS" enabled="true">
<connection-url>jdbc:mysql://localhost:3306/test</connection-url>
<driver>com.mysql</driver>
<transaction-isolation>TRANSACTION_READ_COMMITTED</transaction-isolation>
<pool>
<min-pool-size>10</min-pool-size>
<max-pool-size>100</max-pool-size>
<prefill>true</prefill>
</pool>
<security>
<user-name>root</user-name>
<password>mysqlpass</password>
</security>
<statement>
<prepared-statement-cache-size>32</prepared-statement-cache-size>
<share-prepared-statements>true</share-prepared-statements>
</statement>
</datasource>
<xa-datasource jndi-name="java:jboss/datasources/MySqlXADS" pool-name="MySqlXADS" enabled="true" use-ccm="false">
<xa-datasource-class>com.mysql.jdbc.jdbc2.optional.MysqlXADataSource</xa-datasource-class>
<xa-datasource-property name="ServerName">
localhost
</xa-datasource-property>
<xa-datasource-property name="DatabaseName">
test
</xa-datasource-property>
<xa-datasource-property name="User">
root
</xa-datasource-property>
<xa-datasource-property name="Password">
mysqlpass
</xa-datasource-property>
<driver>com.mysql</driver>
<xa-pool>
<is-same-rm-override>false</is-same-rm-override>
<interleaving>false</interleaving>
<pad-xid>false</pad-xid>
<wrap-xa-resource>false</wrap-xa-resource>
</xa-pool>
<security>
<user-name>root</user-name>
<password>mysqlpass</password>
</security>
<validation>
<validate-on-match>false</validate-on-match>
<background-validation>false</background-validation>
</validation>
<statement>
<share-prepared-statements>false</share-prepared-statements>
</statement>
</xa-datasource>
<drivers>
<driver name="com.mysql" module="com.mysql">
<xa-datasource-class>com.mysql.jdbc.jdbc2.optional.MysqlXADataSource</xa-datasource-class>
</driver>
</drivers>