

Most registrars have some form of whois protection now, so the only people who can easily see it are the registars themselves (and the government that controls them).
Assuming you’re paying for a domain using real money, they’ll need your information on file as part of the online payment anyway, so using a fake id doesn’t really hide anything from them.
It’ll still slow them down and reduce load on your server. I also think many of these crawlers focus on volume; time spent computing the hash is time not spent crawling someone else’s site.