You always have to deploy a *-ds.xml file. Where you put it is up to you. You can include it in the META-INF directory of your EAR file, however, I would not recommend doing this. The *-ds.xml file was meant to allow for dynamic reconfiguration of JCA adapters. Pooling parameters, config properties etc can all be modified on the fly when the *-ds.xml is external.
Note, your adapter by default will only be bound into the java:/ namespace and is only available internally (ie not outside of JBoss). So, as far use is concerned only those application components deployed locally will have access to the adapter.