According to "H-13 Sioux - Mini in Action" by Squadron/Signal the Army used H-13B's, C's, D's and E's in Korea for Medical Evacuations.
Surprisingly, the Surgeon General of the Army in Korea only had about a dozen of these aircraft in his command. There were 4 aircraft assigned to each MASH unit, and there were only 3 MASH units in Korea. I read the same paragraph over 3 times to make sure I understood it.
It's a great little book. I only paid $1.99 for it used. Here's a link to it, but the price must be wrong. It's a tiny little book, but it has alot of useful info and pictures.
http://www.amazon.com/Bell-H-13-Sioux-Helicopter-Action/dp/0897473450/ref=sr_1_1/002-7491660-6907223?ie=UTF8&s=books&qid=1186468818&sr=1-1
The most interesting part was the H-13's development into a gunship and deployment as such in the early stages of US involvement in Vietnam.
Semper Fi,
Chris