No, it is per varnish cluster.

I'd like to expand webrequest_source to many more partition types than it currently has, but at the moment doing so requires a lot of administrative overhead dealing with oozie jobs.

I assume Graphoid requests are being served by the varnish text cluster, yes?

@Ottomata, the graphs are coming from the sca cluster, and exposed as two endpoints:
https://graphoid.wikimedia.org/www.mediawiki.org/v1/png/Extension%3AGraph%2FDemo/1686336/1533aaad45c733dcc7e07614b54cbae4119a6747.png
or
https://www.mediawiki.org/api/rest_v1/page/graph/png/Extension%3AGraph%2FDemo/1686336/1533aaad45c733dcc7e07614b54cbae4119a6747.png
But only the second request gets logged in varnish

What varnishes serve that first endpoint?

Might need to ask @mobrovac or @GWicke about that, but I have moved everything to the second endpoint a few days ago, so it is no longer being used.