Just a slight correction, the list of countries and their limitations on this forum is pretty much for doctors wishing to practice medicine in the country on a permanent basis and for profit. I am rather sure developing and underserved countries won't deny DOs the chance to practice while doing mission or volunteer work. Even MSF accepts DOs for foreign relief work.
For example, I have done volunteer work in Honduras and have some Cuban doctor friends who are practicing there on a permanent basis. They had to complete the 2 years social service work before being fully licensed in Honduras as the list says on this forum. However, for myself, I am just about to start medical school and I was allowed to do a bunch of shadowing and volunteer work in the local hospital with just the hospital director's permission. Once I have my DO I plan to do even more work there and I anticipate no problems at all.
~Nate