Willem Ha. If he's going to be in and out the OA is the better. Don't have to stick 800k in a Thai bank account and can use home country insurance OR self-insure.
Craig Murray. It has happened but only through people not knowing the right procedure to follow which is to arrange for your supervising hospital to provide a "can't travel" certificate and getting it delivered to immigration with an application for medical extension
Yasemen Kurttas. If you're teaching on a volunteer basis you can get a non-O volunteer visa but will still require a work permit. The school/foundation you are volunteering through can help you with the process
George Marinkovich..If he can activate the OA visa he doesn't need to transfer money to Thailand. This can only be done by entering the country with the visa. Getting an O visa in-country means transferring 800k into Thailand