Replace potentiometer in Dart Controls 90vdc motor controller with raspberry pi
I suspect that injecting a voltage into the wiper wire from a DAC and a buffer will work. What won't work is a digipot of the type you linked - they are only rated for 5.5V max despite the digital inputs being capable of 12V+.

This also needs to be an isolated solution but you may find that there is enough power from the outer two pot wires to power the DAC and op-amp. This just leaves digital control of the DAC via a digital isolation chip like an ADuM3401: -



It will need a little bit of testing first to ensure that adding say 1k across the pot doesn't significantly reduce the 6.5 volts. Then try injecting a dc control signal from a power supply between most negative pot position and wiper. If this all seems to work you should be OK.