Why should SuSE be on the line for supporting nVidia, rather than nVidia itself or your hardware supplier? Or is SuSE now also selling corporate computer hardware?

Because its in scope for their support license that you're paying them for.

nVidia is neither Java nor a web server.

https://www.suse.com/support/policy-products/

I'm unsure what argument you are trying to make here? The page you linked makes no reference at all to nVidia. And directly below where it mentions Java (web servers are not mentioned at all, only web browsers), it also excludes:

  * All 3rd party binaries such as fonts, sounds, artwork and branding
And further down, it also excludes:

  * Packages without public available source
  * Packages with non-Open Source license
I'm not sure if SuSE considers nVidia drivers to be 3rd party or not, but they are definitely without public available source and without an Open Source license.

Because SuSE has YES-certified the hardware it's running on.