AFAIK classloaders are supposed to by hierachical. So the ear classloader is the parent of the classloader for the war and the ejbjar. You can only inherit from a parent (or the parent of the parent) classloader. As a result, an ejbjar cannot inherit the classloader of a war file, which is what you're trying to do. Proper design in this case would be to place shared libraries in side the ear file and define them as java modules in the ear's descriptor.
However, the UseJBossWebLoader=true in 3.2.3 does give the EJB deployment visibility into the WEB-INF/lib so it is possible to do.
Your suggestion works also.