I'm an MS-IV at KCOM. There are several opportunities to do your clinical rotations outside of Missouri. In fact, most students end up outside of MO. To answer your questions about regions...during your second year at KCOM, you and all your classmates will participate in a "match" which will determine which hospital/hospital system you will do most of your rotations at. You will NOT match to a region. The Arizona site is a little different because it's comprised of several hospitals. I believe the colorado region is a little like that too. But, like I said, most students will match to a specific hospital. Oh, and I think that the first choice match rate is usually around 92-95% so most folks are pretty happy - even if they match to their second choice.
In my experience/feedback I've gotten, not all sites are created equal (how could they be??). Which site to rank as #1 is a multi-factorial choice for most people (proximity to family, weather, diadactic strength, how many and how large the post-doc training programs are at a given hospital, etc, etc).
Hope this helps.