Server uses the logging subsystem we "inherit" from WildFly, and it uses the JBoss LogManager. See [WFCORE-482] Add log4j2 support for WildFly - JBoss Issue Tracker for discussion related to log4j 2.x in that context. Maybe jamezp can provide more information.
There is a facade from log4j (1.x) to JBoss Log Manager. There is not a facade to delegate log4j2 to the JBoss Log Manager at this time. From a WildFly perspective you can include a log4j2 configuration file in your deployment and include the log4j2 library and all should work. You just don't have central runtime configuration tools.
James R. Perkins
Just a note for people that just want their application using log4j2 to log to the wildfly server log (for example because of using a framework struts2 which is using log4j2)
The answer is here: