As of today, I checked in a full implementation of the JAX-WS wsgen tool. This work includes a full API and SPI, as well as an ant task and command line tool.

The WebServiceGenerator API is available here:
http://labs.jboss.com/file-access/default/members/jbossws/downloads/api-docs/org/jboss/ws/tools/jaxws/api/WebServiceGenerator.html

The WebServiceGeneratorProvider SPI here:
http://labs.jboss.com/file-access/default/members/jbossws/downloads/api-docs/org/jboss/ws/tools/jaxws/spi/WebServiceGeneratorProvider.html

A custom provider can be specified using the system property "org.jboss.ws.tools.jaxws.webServiceGeneratorProvider". This property is also available as static public field on WebServiceGenerator.

The command line tool documentation is available here:
http://labs.jboss.com/file-access/default/members/jbossws/downloads/api-docs/org/jboss/ws/tools/jaxws/WSGenerate.html

The ant task documentation is available here:
http://labs.jboss.com/file-access/default/members/jbossws/downloads/api-docs/org/jboss/ws/tools/jaxws/ant/WSGenerate.html

The test case that demonstrates the API is located here:
http://fisheye.jboss.com/browse/JBossWS/trunk/jbossws-tests/src/main/java/org/jboss/test/ws/tools/jaxws/WebServiceGeneratorTestCase.java?r=2156

-Jason