Hello Daniel,
I've had that same problem, and resolved it by setting the "Connector Classloading Policy" to "global" in Glassfish.
You can do it from the Glassfish admin console by navigating to "Configuration > server-config > Connector Service". The default is "derived" since Glassfish 3.1, I believe. My understanding is that Glassfish 3.1 implements the version 1.6 of the JCA specification, which (as opposed to JCA 1.5) does not require any more that the classes in a resource adapter be made available to all applications.
It should be possible to use the JPPF connector with the "derived" class loading policy, but I haven't figured out how to make the connector classes available to the JPPF demo web app, without adding them to the server's classpath. Glassfish is definitely not the app server I'm the most proficient with

If you have any suggestion, I'll certainly be happy to read it.
Sincerely,
-Laurent