Poultry grow immunity to cocci as youngsters. It is present in the digestive tract of all birds and as they age, they develop the ability to control it on their own. So as you raise your quail, they will either die from it, or automatically become immune to it.
There is nothing wrong with keeping quail on dirt. I have kept quail in an aviary style environment for 6 years with a dirt floor covered in different types of litter. As long as you don't crowd them in too much and rake up the litter when it gets too pooped up, then the quail will do just fine.
The problem comes in when you allow too much moisture to get in...such as rain or snow. Bacteria and fungus love warm, moist conditions. So if you can keep it as dry as possible, you will be able to control the disease and parasites.