Yes, I had heard of him, and presumably so had the Apple employees who assembled a letter that quotes him extensively: https://www.theverge.com/2021/5/12/22432909/apple-petition-h....
I don't see any reason to doubt that plenty of people at Apple had heard of him and read the book, other than a self-regarding faith that people you disagree with can't possibly know something you don't.
[1] https://www.theverge.com/2021/5/12/22432909/apple-petition-h...
Examples of the background research they could have done:
1. talk to any of the employees who organized the petition
2. read his book! It's widely available! This is a guy whose hiring was literally a positive news story yesterday https://www.businessinsider.com/apple-hires-chaos-monkeys-au.... When you hire people who are going to be news you do a little background. It's a short book! Apple screwed up!