Although we allow TimerService to be injected into beans through @Resource, we don't really pull it from the java:comp/TimerService. Infact, java:comp/TimerService is not really bound for any of the EJB types. The injection works because of a special org.jboss.injection.TimerServicePropertyInjector which bypasses the ENC during injection.
TimerServicePropertyInjector will henceforth be deprecated and TimerService injection should henceforth happen through java:comp/TimerService.