I am having some issues with using JBoss TreeCache in WebSphere due to the JBoss TreeCache dependency on JBoss JMX. I know this isn't a WebSphere support group, but I though I would bring it up since you are targeting this library for portable use.
WebSphere heavily uses JMX for administration and it will only accept its version of the javax.management API. In my application I have setup the class loader hierarchy to load my application classes BEFORE the container classes (PARENT_LAST class loader mode). Since JBoss Cache is in my class loader the JBoss JMX JARs will be the ones which are visible to my application. I would like to register MBeans with the WAS MBean server, but I am prevented because I cant cast the WAS MBean server instance to the JBoss version of the JARs.
Also, I have considered moving the JBoss Cache up the class loader hierarchy to the container, but to do so I would have to unseal the WAS jmxc.jar and override it with the JBoss JMX implemenation as recommended by JBossCacheAndWAS Wiki. I believe this would cause instability in the container at best and render the WAS MBean server useless at worst.