I don't know if it was intentional, but the fact that Guzma actually has one of these things really does give a good indication that he isn't really as bad a guy as he makes out. These things are not easy to train. They start off weak as water bail out of a situation if they get below half their HP. They can't be trained by being headstrong. They need patience. Guzma would not be able to get one of these things unless he willingly put in that level of patience and understanding you need to train a pokemon like this. It's a small detail, and I'm not sure if the developers meant it, but it really does speak so much for his character.