How many professors are there in technical fields with no degree whatsoever? Peter Beck has recently been appointed an Adjunct Professor in Aerospace Engineering at the University of Auckland. As you know, Peter Beck is the founder of Rocket Lab, which has put payloads into space, but Peter Beck also never attended college and even dropped out of high school.

How many Adjunct Professors are there in technical fields like Aerospace Engineering without any college degrees? How many high school dropout professors without degrees?
I don't have numbers, of course, nor even proportions, but I suspect that the number is small. 

But more important is the question of how such a person would be hired and what sort of position they could hold. The problem is that a school or university wanting to employ such a person needs some assurance that the person is competent for the position. Not holding any degrees makes that more difficult in general. 

But some people have excelled in a field with no formal education. That isn't especially unusual, actually, but not a lot of them will want to teach. But some will. Many will want to do it only part time and money isn't the driver for them, so a position as an adjunct can be attractive both to them and to a university. But no one will be looking at it as a career path. 

I suspect that Harvard would be happy to have Bill Gates teach a course occasionally - probably not in BASIC language, though. 

Luminaries in a field are probably offered such courses fairly frequently, I'd guess. But especially if the institution is looking to establish a long term relationship with future funding in mind.