We don't recommend deploying your applications alongside Keycloak for several reasons:
* Keycloak is not just for JEE applications
* Applications can interfere with Keycloak which would result in hard to debug issues
* Keycloak overlay only supports a specific version of WildFly. You may not always want to upgrade the WildFly used by your applications when upgrading Keycloak
* Keycloak requires specific configuration of the underlying WildFly instance. Any changes you do may break it and again cause hard to debug issues
In the supported version of Keycloak there is no overlay at all, only the standalone distribution. The overlay distribution is purely meant as a convenience thing for JEE developers.