Apparently not, otherwise there wouldn't exist something like "The PostgreSQL Global Development Group".

Anyone trying others to adopt their products is a vendor, regardless if they are commercial or open source.

Also Linux is just a kernel, naturally it needs a vendor like RedHat or Canonical to provide an actual product.

Postgres is a RDMS already out of the box.

PGDG is effectively an industry consortium of the aligned interests of corporate members—i.e., the vendors. Things don’t “happen” at the level of PGDG, any more than things happen at the level of the UN. Both organizations are there to create opportunities for consensus between members; but in both organizations, it’s the individual members that then go on to actually do things, mostly without one-another’s help.

The PGDG doesn't really exist in the form you imagine. There certainly isn't corporate members or such. It's just a descriptor for all the developers together - it's not even a well defined legal entity.

Right, the members aren't the corporations; rather, the members are the developers, who happen to mostly work for the corporations that serve as vendors. That's what "corporate membership" looks like in FOSS.

E.g., in most Apache projects originally donated from a corporation, that corporation's employees usually still constitute a majority of the developers.

The corporation(s), in such cases, aren't sponsoring the project in any strict technical/legal sense. Rather, the project is steering and constraining the corporation(s) in their development efforts on their forks/extensions of the project codebase, determining through the project's core maintainership's decisions, what will be accepted/upstreamed from those corporate forks/extensions into the open core, vs. what will have to remain in those forks.

See: Redis vs. Redis Labs; CouchDB vs. Cloudant; Apache BEAM vs. Google Cloud Dataflow; etc.

As answered, pgadmin is first class and supports debugging.