I am pretty certain people have got the DTV teaching online to students outside of Thailand. A guy I know teaches Vietnamese and Japanese. The Viets in the evening and Japanese businessmen 5am to 7am Thai time. Free all day after that till evening classes.
If they hold certain visa types. Have a look on the VFS website - it has the info. A lot of visas are outsourced to VFS these days. UK is and quite a few others
Some visas you can only apply in your home country or where you have long term visa/residency ie a Burmese could not apply for a Schengen Visa while in Thailand on a tourist visa - in face most non-Thais could not.