Got a filter pn with the sensor (or a model number for a machine that requires it)? The John Deere 9R 540 replacement parts guide doesn't seem to show anything with a sensor and that's a new large articulated machine:
https://www.deere.com/assets/pdfs/common/qrg/rx535024.pdf
View attachment 817112
As for the rest, Deere can deny warranty coverage if using an aftermarket part caused the problem, but they CANNOT legally require that you use their parts, their service people, etc unless they are providing them at no cost to you.
They can't flat out deny warranty coverage because you used aftermarket parts that met Deere specs (ie: if you used an API CK-4 oil of the correct weight and lost a turbo charger in the warranty period they have to cover it unless they can prove that the oil was the cause).
It looks like they are instead using the carrot method where if you use their oil and their filters you can extend the oil change info by 500 hours (from 1500 hours to 2000 hours).
That alone would probably make it worth it to somebody who can't afford to have downtime in their busy season and to get another 500 hours out of the 16 gallons of oil that the 13.6L motor in some of the 9R machines uses.
Aaron Z