Tenuous ground. When you buy the product, it needs to work. Part of the product is the firmware. If the firmware needs an update, the original purchaser ought to be entitled to that update, or a refund of the hardware that didn't work properly when they bought it. Selling someone a defective product and then trying to use copyright on a fix to wrest control doesn't seem a legitimate business practice.
There's a body of consumer protection law that would generally be more supportive of this position although these days there are signs it is becoming less effective. In part, the consumer is not given the chance to accept or deny EULAs prior to purchase, and because it is recognized that a consumer is unlikely to be versed in legalese and has been primarily guided by advertisement and marketing.
That's for consumers, which Nvidia's EULA change states as being the licensed case for its Geforce drivers. Even then, I think some amount of imperfection is acceptable in the end. There are still driver bugs and I've not seen a mass of successful lawsuits every time a card has issues in a game.
An enterprise that builds data centers, manages multiple employees and large-scale contracts is not an unsophisticated user. It's navigated untold numbers of regulations and contracts already, and in other instances Sakura Internet is likely using the same sorts of complex legal procedures in negotiations to its own benefit.
In a context where there is a professional or enterprise interest, there is more precedent to the idea that there can be more complicated contractual obligations or additional conditions, just like how many software packages have home, education, and professional/enterprise variations with audits or tip lines to catch companies pirating or abusing the license.
Being able to say how copyrighted software can be used is something that has been accepted for some time, and niche or technical tools and software have not had their sometimes heavy restrictions challenged.
If there's old drivers Nvidia probably cannot forbid their use since the license at the time was more permissive. Nvidia could argue that in-house or open-source software is an option, if Sakura Internet wanted to do more than just find a loophole in Nvidia's segmentation on the cheap. Downloading new drivers is asking the copyright owner for permission to receive a copy, and Nvidia is able to add conditions. The right to have a say over how one's work is used is granted to any copyright holder, so it would be an uncommon case to take that away for anyone, not just Nvidia.
Nvidia can argue that the product still works in the use cases it considers valid, and there are any number of products that have tags or provisions indicating they are only for a specific kind of use.
Antitrust could be involved if Nvidia was making moves into Sakura Internet's market, but if it's still selling Quadros and Teslas to whomever would buy them it would be a harder case to make. Nvidia could argue they could switch to AMD, and if Sakura Internet objects with something like "but AMD's software is terrible for our datacenter service", then Nvidia would argue that it sounds like good drivers are something worth paying extra for.
One possible new area where copyright might have less precedent is if Sakura Internet tried to write its own drivers and Nvidia had some kind of code-signing or secure boot measure like AMD's PSP that was made to block the usage, the back and forth on circumventing copyrighted encryption measures used to lock out otherwise normal use is not as clear.