I can’t verify this claim, but given my personal experience it makes perfect sense. I run a 980 Ti alongside a 950 in my hackintosh tower and graphical glitches on the desktop happen pretty regularly despite both cards being perfectly healthy.
The other thing is that historically, Apple has been unwilling to differentiate the drivers between consumer and workstation cards because generally speaking that concept is kind of silly. Everybody should have workstation-class stability, not just those who shell out 3-5x more cash for a workstation card. It’s obvious why Nvidia would take issue with this,
Then Apple needs to dig down into their pocket, maybe they’ve got some extra money there, and solve this problem.
The Nvidia web drivers are not great but there are so many factors that could be producing those glitches.
I've built about a dozen hackintoshes since 2010 and while I've experienced many problems I personally haver never seen graphical glitches.
I don't think it's fair to expect the same level of reliability from a frankenstein you've built yourself than a commercial product.
I think in my case specifically the graphical glitches are caused by having dual GPUs. That’s a somewhat uncommon configuration, but not so strange as to not test for.