It is not possible to have different themes for different tabs AFAIK. I believe it would be possible to use the ST-API events on_activated, and on_load, to dynamically attach different themes according to the current file type. Although, I suspect this would impact the overall performance of ST.
Alternatively, a key-binding or command could be created to switch between themes. I believe there might be a Package already available that does something similar.
"I'm here to save your life. But if I'm going to do that, I'll need total uninanonynymity." Me Myself & Irene.