I personally think its completely stupid to add a hiring CTA mainly because it takes away from your main CTA which is to convert the visitor into a customer. But if it doesn't hurt your funnel then there's no harm of adding it.
I think it depends a lot on the stage a company is at, their goals, and the types of people visiting the site. For us (Glider), being pre-product, most site visitors are potential investors and potential employees. So a hiring CTA makes some sense.