I was able to follow these instructions and get OpenAM working using the J2EE agent. However, i ended up backing it out in favor of putting Apache in front of Alfresco and using OpenAM to secure Apache instead (you could still have it secure the tomcat container with Apache in front).
There are some pieces the topic posted above that are not 100% straight forward, and I think it is missing an exception in Tomcat or Openam to allow Solr to index properly. However, the Apache agent and Alfresco external auth is pretty straightforward.