Well, I bought a food dehydrator. Every site told me to dry only lean meat, and so I did until now. However I was thinking of drying some ham in larger chunks to hopefully get sort of prosciutto substitute. I know that the fat can go rancid which is why I intend to eat it within a month and store it in a fridge and I know it won't taste as good as the original. Do you think it's safe?
Yes. It may be fine for immediate consumption.
The problem is the air flow from the drying itself can also accelerate the oxidation of the fat.
When I have dried fatty meat the fat already tasted a bit off.
This is a matter of quality, not safety. If the fat isn't objectionable to you after drying then it is fine. As you said, you should expect the fat to go off and eat it soon.