Impaction from swallowing substrate is a legitimate possibility, especially if the snake is small or the substrate pieces are large. However, IMHO, it's not a great concern. Dums are big animals, so they'd have to swallow large or numerous pieces to create a health concern. If the rodent is dry, little should stick to it and you won't have anything to worry about. I don't use Reptibark myself so I'm not sure if it comes in different grades or not. I use aspen. It's cheaper, readily available, safe and clean. I feed my snakes in their enclosures and haven't had problems with them swallowing substrate.