at my institution the chairman's letter restates your evals from your clerkship, is written by the clerkship director and then signed by the chairman of the pediatric department. they have it down pretty pat, and i bet if you ask your clerkship director he will know very well how it is handled
i found out about all this by asking the clerkship director (whom i met with and gave my personal statement and CV to). i dont know who requires it, i know ill get one, and i know a lot of programs that dont care about it here in the midwest. good luck