Laurent has a great posting on Hiring Programmers. Note that he doesn’t say people have to be great writers. On the contrary, the bar is fairly low: awareness of spelling and typos, introduction, structured discussion, conclusion — that’s it. My kids practice this kind of writing all the time in school (in preparation for the standardized tests they need to pass in order to receive a high school diploma — MCAS for those of you in Massachusetts).
I agree with Laurent, don’t forget to add an audition. But definitely, ask people who need to be able to communicate in writing to write for you.