Although snake mites do go through a stage where they are tiny and white, what you are describing are probably something different. I forgot what they are called, but they are often found in wood/bark mulches and are harmless to the snake.
Are they fast moving? Like able to cross an inch in 3 seconds? Mites are sloowww. That is one way to tell. Mites are roundish, where the wood bugs look more elongated.
At any rate, you can wash the substrate to get rid of most of the bugs then dry it in the oven if you want to kill any eggs.
Check your snakes for adult, feeding mites (black and round). If you don't see any crawling around the snakes' eyes, you probably do not have mites. If you do, post back, and we will help.