The sample oracle-ds.xml files should have a comment in them that the XA samples would be better in most conditions. The DS samples will only support ONE datasource in a transaction at a time. Any attempt to connect to two separate Oracle (or other non-XA datasource) at the same time will fail.
This is in the DataSource samples for 4.2.2.GA, as well as JBoss 5.0.0.Beta4. It would probably be a good idea to add a line along the lines of;
<!-- WARNING: This sample is for backwards compatibility with pre Oracle10g only.
Please see the oracle-xa-ds.xml file for an up to date sample. -->
NOTE: The Wiki's are also out of date and confusing for this topic. (Another thread).
Should I open a JIRA Issue on the examples?