About 50% of my job is literally shipping items/parts to customers. I use FedEx, DHL, USPS and UPS respectively and REGARDLESS of who you use, as long as YOU, the shipper, package the item properly, damage will be non-existent or minimal. It stands to reason that as long as the item is 'bundled" in a way that negates travel damage you're fine. Granted there are instances when it's out of your control BUT before an item is shipped, the shipper can guarantee with 99% certainty the item will arrive at its destination in perfect working order.
Using a bubbled mailer to send a slabbed book is perfectly safe, as long as the book is secured inside something else before going into the mailer. Simple as that.