Seam REST requires a CDI implementation. Are you using Weld Servlet with your application? Weld's docs says Servlet injection is supported with Tomcat 6. I am not sure what's the situation with Tomcat 7 and Listener injection, though.
If you open a JIRA issue I can try to make the module less EE6-dependent.
I configured the project according to the description in the doc.
In servlet 2.5 container(tomcat 6), there is almost no configurtion, a Applcation(and registered in web.xml), but in servlet 3.0 container(tomcat 7), the SeamRestStartup(with a @WebListener annotation) was invoked automatically.
But i noticed weld info when tocmat starts up.
It indicated that weld can not inject object into Listener.