In EAP 6.4 , sub deployments were accessible before all Singleton's PostConstruct were finished, this was fixed via [1]. After this fix if an exception was thrown from PostConstruct, then the whole deployment was in a failed state as well. EAP 7.0 works the same as EAP 6.4 after the fix.

In EAP 7.3/7.2/7.1 when the Singleton throws an exception, the sub deployments are accessible.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1310908

EJB 3.1 spec, section 4.8.1:

If the Startup annotation appears on the Singleton bean class or if the Singleton has been designated via the deployment descriptor as requiring eager initialization, the container must initialize the Singleton bean instance during the application startup sequence. The container must initialize all such startup-time Singletons before any external client requests (that is, client requests originating outside of the application) are delivered to any enterprise bean components in the application.