Do I have to bury the fermented waste or could I mix it with soil on top of the ground and let it finish its decomposing process there?
Its better to bury the fermented food waste. This keeps it away from curious animals, and also keeps it from drying out in the sunlight, which will make it harder for the soil life to process it into good finished compost. Most of the life in the soil lives below the top surface, so burying it makes it more readily accessible to those organisms.
Happy composting from Nick at Bokashi Living!