I'm defining an ha xa datasource for two DB2 data sources, but this fails. The reason is that org.jboss.resource.JBossResourceException.HAXAManagedConnectionFactory tries to use the setURL method of the defined xa datasource class (com.ibm.db2.jcc.DB2XADataSource), which does not exist. For a non-ha xa DB2 datasource, server name, port number, and database name is defined independently.
I've checked in subversion and the same behavior/code seems to exist in JBoss AS 4.2.2. Also, I check the latest version av DB2 jdbc drivers (v2.11.24) and they do not have the setURL method either.

Below is my ds definition (ha):
<datasources>
<ha-xa-datasource>
<jndi-name>JNDI_NAME</jndi-name>
<xa-datasource-class>com.ibm.db2.jcc.DB2XADataSource</xa-datasource-class>
<xa-datasource-property name="URL">jdbc:db2://HOST1:PORT1/DBNAME1|jdbc:db2://HOST2:PORT2/DBNAME2</xa-datasource-property>
<url-property>URL</url-property>
<url-delimeter>|</url-delimeter>
<xa-datasource-property name="DriverType">4</xa-datasource-property>
<user-name>USERNAME</user-name>
<password>PASSWORD</password>
<isSameRM-override-value>false</isSameRM-override-value>
<track-connection-by-tx/>
<transaction-isolation>TRANSACTION_READ_UNCOMMITTED</transaction-isolation>
<max-pool-size>50</max-pool-size>
</ha-xa-datasource>
</datasources>

The same (well just one database) if ha is NOT used:
<datasources>
<xa-datasource>
<jndi-name>JNDI_NAME</jndi-name>
<xa-datasource-class>com.ibm.db2.jcc.DB2XADataSource</xa-datasource-class>
<xa-datasource-property name="ServerName">HOST</xa-datasource-property>
<xa-datasource-property name="PortNumber">PORT</xa-datasource-property>
<xa-datasource-property name="DatabaseName">DBNAME</xa-datasource-property>
<xa-datasource-property name="DriverType">4</xa-datasource-property>
<user-name>USERNAME</user-name>
<password>PASSWORD</password>
<isSameRM-override-value>false</isSameRM-override-value>
<track-connection-by-tx/>
<transaction-isolation>TRANSACTION_READ_UNCOMMITTED</transaction-isolation>
<max-pool-size>10</max-pool-size>
</xa-datasource>
</datasources>