NVIDIA Capture software is a program which is protected by copyright. That means that it cannot be used at all except with permission of the software creator. The rights-holder is allowed to set whatever conditions it wants in the permission agreement (the above-linked license). They can let you use it if you pay, or for free; they can let you use it only on certain products, or with no restrictions. The license specifically allows you to
install, use and reproduce the software delivered by NVIDIA, make
modifications and create derivative works of sample source code
software delivered by NVIDIA and use documentation delivered by
NVIDIA, provided that the software is executed only in NVIDIA GRID,
Tesla or Quadro 2000+ hardware products that you separately obtain
from NVIDIA or its affiliates, all to develop, test and service your
products (each, a “Customer Product”) that are interoperable with
NVIDIA GRID, Tesla or Quadro 2000+ hardware products
So they have commercially created software that enhances the operation of their hardware product, and only allow the software to be used on their hardware.
This may be legal under current anti-trust law. The statutory language is not clear, and legality is determined via case law. The way to determine if it is currently illegal is to inspect the record of similar cases, especially US v. Microsoft, pertaining to the relationship between the OS and their browser. It is possible that a court would find NVIDIA to be in an analogous dominant position. The Microsoft battle was not subjected to an ultimate court finding after an initial finding against the company, and was settled without establishing a distinguishing precedent, after the company prevailed on the highest appeal. That appeal did not bring forward any legal principles that would tend to render NVIDIA's policy illegal, but one can always pour over this case to see if there is anything applicable, if one decides to pursue NVIDIA on similar grounds.