Putting aside whether it's best to use them as the company intended, random pronounceable word sequences should be strictly-better than hex/ASCII ones. (Presuming the company isn't limiting "answers" to unreasonably short character lengths.)
Another risk is that someone will call up and say "it's just a bunch of random stuff" and the customer service rep will go: "Okay, that's right, moving on..."
Another risk is that someone will call up and say "it's just a bunch of random stuff" and the customer service rep will go: "Okay, that's right, moving on..."