Yes, CMP works with Sybase.
Just as for BMP, you will need to define a Sybase datasourse in the jaws.xml file and then reference that datasource in the ejb-web.xml file. You also need to drop a sybase-service.xml file into your server's "deploy" directory. YIn addition, you will need to copy Sybase's jconn2.jar into the desired configuration's "lib" directory.
I've attached a sample sybase-service.xml file. It needs to be edited, to set the appropriate account name, password, and url info for your Sybase installation.
I believe jaws.xml is 'a legacy deployment descriptor' for applications using CMP 1.1. jbosscmp-jdbc.xml is the new deployment descriptor used in JBoss3.x for container managed persistence configuration.
Oops. Sorry. I should have provided the caveat that I'm a newbie. Also, the sybase-service.xml file that comes with the JBoss distribution, and is found in directory docs\examples\jca, is a much better place to start than the example that I attached.