Close.
It's more accurate to say that the EE4J PMC provides oversight, guidance, best practices, governance, etc. for all of the open source projects that are part the EE4J Top Level Project. That is the Top Level Project is part of the organizational structure, and the PMC is the actual group that provides the services. I may be splitting hairs (it's common to conflate the PMC and the TLP).
The PMC provides governance for all projects, regardless of what the projects actually do. So this includes both specification and implementation projects. It's also the PMC that oversees the release process (with help from the EMO).
The Jakarta EE Working Group (via the Specification Committee) is responsible for taking the specifications produced by the open source projects and designating them as "official" (I really want to say "promote", but the marketing folks get confused when I do that). They are further responsible for managing the process by which implementations of the specifications are certified.
The Jakarta EE Platform is just one of the specifications. It happens to be what is referred to as a "profile", so it's a special specification, but there are other specifications that are also special.
There are only three committees in the Jakarta EE Working Group: Steering, Specification, and Marketing and Brand. The Eclipse IP Advisory Committee is not part of the working group.
The easiest way to think about is it that the PMC works at the "committers and projects" level, and the working group works at the "companies and business" level.
TL;DR: The open source projects, under the supervision of the PMC, assemble the various artifacts (spec document, API, TCK, implementation) and hand them off to the Spec Committee to designate as official and implement the certification process.
Wayne