In the POM file for our quickstarts/cxf/camel-cxf-contract-first example, we configure the Maven codegen plug-in with additional JVM args as follows:
The additionalJvmArgs option is set, but there is no fork setting here. But according to the CXF docs 
"Additional JVM args set on the forked process if fork is not false"
We need the fork option to be set to once or always, otherwise additionalJvmArgs is ignored. In other words, the correct configuration could look like:
In email correspondence, Freeman(Yue) Fang has confirmed to me that the default setting of fork is false, so that the JVM args setting is currently being ignored.