Honestly, anything non-food that your horse might ingest has the potential to harm or kill them. One of my donkey-owning friends on Facebook just removed a deflated balloon with ribbon attached from the stomach of one of her donkeys, it caused him to colic and nearly killed him. Ingesting a non-food substance or foreign object is going to cause problems, period. He could get in just as much trouble from eating too much grain or spring grass, chewing wood on the fence or in his stall, eating moldy hay someone didn't check, eating a piece of trash that blew into his pasture...the list goes on.
If the horse is eating his bedding, then either it needs to not be used for HIM specifically, or he needs to be on something he won't eat or is safe for him to eat, such as straw. If you've used it without incident in your stalls so far, and your horses don't snack on their bedding, I don't see it being an issue going forward.