Not exclusively. ARM's roadmap is driven by what all of their customers want, not just Nvidia.

There doesn't appear to be sufficient profit margin in the industry for too many greenfield, non-reference custom implementations.

So if Nvidia-ARM sticks out a reference implementation or architecture choice that's beneficial to Nvidia, there's limited capability for others (Apple, Cavium/Marvell, Qualcomm, & Samsung?) to strike their own path, and they'll certainly be paying steeply to do so.