hotdeploy of individual classes that are EJBs ? No, that is not possible.
hotdeploy of a single module/archive ? Yes, that is possible - simply redeploy it (right click, full publish) or touch the descriptor (in JBT there is the "touch" button to do this)
You do *not* need to restart the full appserver if your app is clean (i.e. no usage of classes from the bootclasspath)