You should take a look at JBWS-2206 and related issues JBWS-1714 and JBWS-1837.
From the information I could gather, JBoss internally uses Metro (the RI) for JAX-WS. I'm not very sure about this, but it appears that Metro reads WSDLs, if provided via the wsdllocation attribute, using the classloader, thereby making META-INF/wsdl of the EJB JAR a safe choice to place WSDLs. The example file in JBWS-2206 would help as a reference.
Update
A thorough overview on how to provide your own WSDL is present in the JBoss forums.
Update #2
The JAX-WS specification, gives a better idea on why this is the case. In the section 5.2.5.3 Use of @WebService(wsdlLocation) and Metadata, one can find the specification stating that
The value of the wsdlLocation annotation element on an endpoint implementation class, if any, MUST
be a relative URL. The document it points to MUST be packaged with the application. Moreover, it MUST
follow the requirements in section 5.2.5.4 below (”Application-specified Service”).
Furthermore, it states that
A JAX-WS implementation MUST patch the location attributes of all wsdl:import and xsd:import
statement in local documents that point to local documents. An implementation MUST NOT patch any
other location attributes.
defining how the generated WSDL should appear.