re: "Re: Can you write off a hourly freelancer's time when they live outside the US?"
Yes, of course.
re: "I've worked with a freelancer who lives outside the US this year. Am I able to write this off on my taxes?"
re: "...do I need to send something to them? Any documentation."
You do not necessarily need to send something to them.
There are MANY ways to file taxes. Keep in mind that you are not hiring employees. When you hire freelancers, your expenses can be classified as business-to-business expenses. Among other things. Your local tax experts and authorities will be able to provide you different strategies and answers.