Check your hsqldb-ds.xml definition. Normally, the Hypersonic service is enabled if you are using the JDBC port based configuration. Otherwise, if you are using the in-process or in-memory configurations, Hypersonic is not actually required and may be commented out. JBoss 3.2.0 used the JDBC-enabled configuration so the default distribution would show the Hypersonic service in JMX-console. This might have changed in your version. YMMV. However, you can confirm this by checking the datasource configuration. This will also show you the binding name expected if your Hypersonic service is operational.
Your suggestion prompted me to look at hsqldb-ds.xml file in the deploy folder. To activate the Hypersonic database service, I changed the file name to hsqldb-service.xml.
Thanks a lot.