It depends on your application. JBoss Cache is not a drop-in replacement for stateful session beans in any way. If all your SFSBs do is maintain back-end state for your applets, then they could be replaced with a cache service (clustered or not) but you will still need some remoting to alow your applet to talk to your cache tier. With EJBs you get this for free, since EJBs are remote objects anyway.
Perhaps you could use a stateless session bean to manage the remote conversation, and this stateless bean could, on the server side, talk to the cache layer.